Two new species of brachiopoda from the Inferior Oolite, Lincolnshire Limestone

47 6

TWO NEW SPECIES OF BRACHIOPODA FROM THE INFERIOR OOLITE, LINCOLNSHIRE LIMESTONE. By HELEN M. MUIR-WOOD, D.Se., F.G.S.

THE Rhynchonellid and Zeilleriid described in this paper occur in the middle part of the Lincolnshire Limestone. This part overlies the well-defined Acanthothyris crossi-Bed of South Lincolnshire and is below the plane of erosion which separates off the Top Beds, referred to as Terebratula and Gastropod Beds, Weldon Beds, or Ancaster Rag, in different localities. The Rhynchonellid, Parvirhynchia kirtonensis sp. nov., occurs in crag-balls or coralliferaus limestone masses near the base of the Kirton cement-shale in the northern part of Lincolnshire. It also occurs in the Wilsford Beds further south near Ancaster, and in a coral-bed in the Ancaster Freestone. The Zeilleriid, Zeilleria wilsfordensis sp. nov., has not yet been found north of the Ancaster district, but occurs in the Wilsford Beds, and in the Ancaster Freestone coral-bed, associated with P. kirtonensis. It is also found further south in Lincolnshire in a coral-bed in the Castle Bytham ' Roadstone.' As it is probable that these two species were not long-ranging forms, the Kirton cement-shale may be correlated with, and considered to be of approximately the same age as the Wilsford Beds, the Ancaster Freestone, and the Castle Bytham 'Roadstone.' The precise age of these beds is still uncertain, but they are probably post-discites-the age assigned to the Buckmani Grit of the Cotteswolds. Comparison of examples of Parvirhynchia kirtonensis sp. nov. and Zeilleria wilsfordensis sp. nov. with forms occurring in the Inferior Oolite of Yorkshire, the Cotteswolds, Somerset and Dorset, has shown that they are more closely allied to the Cotteswold and Somerset than to the Yorkshire species. The specimens were either collected during the Stamford (1938), or Melton Mowbray (1939) field meetings, or obtained by Mr. L. Richardson or Mr. P. E. Kent independently. All the types and most of the specimens examined are preserved in the British Museum (Natural History).

DESCRIPTION OF SPECIES. Family Rhynchonellidae. Genus Parvirhynchia S. S. Buckman, 1914. 1917, Palseont. Ind. (N.S.), III, no. 2, p. 56. GENOTYPE. Rhynchonella parvula Eud.-Desl. SPECIES recognised :-P. minuta Buvignier, Oxfordian; P. pellucida S. S. Buckman, garantiana zone; P. parvula (E.

TWO XEW SPECIES OF BRACHIOPODA.

477

Eud.-Desl.) pre-blagdeni zone of France (fide Roche 1939) and ? garantiana zone of Dorset; P. d. paroula' (Eud.-Desl.) concava zone of Somerset; P. sp. nov., discites zone of Cotteswolds ; P. auriculifera (Richardson & Upton) murchisonae zone, and related form in scissum zone of Cotteswolds. RANGE. Jurassic, Inferior Oolite to Oxfordian. REMARKS. Buckman's (1917) diagnosis of this genus was : "Hypothyrid (beak produced, suberect, foramen circular, tubular, deltidial plates large, conjunct, marginate) ; flabelliform ; capillate, capillae continued over undiplicae [which began as Fig. 28 shows, in the norella stage; dental plates slightly diverging; dorsal scars in a quadriform pattern]." To this diagnosis the following details may be added:Dorsal septum low, not supporting hinge-plates in umbonal region. Hinge-plates not fused posteriorly, inclined dorsally at low angle to horizontal, scarcely differentiated from inner socketridges. Septalium and cardinal process absent. Crural bases given off ventrally. Crura ca1carifer. Pedicle-collar not developed. Parvirhynchia kirtonensis sp. nov. Fig. 42 (1-3c); 43. Syn, Acanthothyris crossi ( in part) Auctt.

DIAGNOSIS :-Parvirhynchia, pentagonal in outline, about 7 mm. long, 8 mm.wide, and S mm. thick; both valves moderately convex, with flattened dorsal fold and shallow ventral sinus well demarcated from lateral slopes. Linguiform extension long, tapering. Umbo suberect, produced, acute, tapering, foramen marginate to auriculate. Ornament of fine growthlines, rarely preserved radial capillae and about I I broad angular costae, rarely bifurcating on flanks, with 3 on median fold and 2 in sinus. Apical angle 130°. TYPE-SPECIMEN :-Holotype from the Lincolnshire Limestone, crog-balls in Kirton Cement-shale, Kirton-in-Lindsey, Lincs., and preserved in the Richardson Collection, British Museum (Nat. Hist.) BB. 6643. Paratype from same locality and horizon [BB. 6632] and from the Wilsford Beds, rst railwaycutting, E. of Ancaster [BB. 3772]. MATERIAL AND LOCALITY :-About 2S specimens from the Lincolnshire Limestone, Wilsford Beds; coral-bed in Ancaster Freestone; crog-balls in Kirton cement-shale, etc., discites or post-discites zone. Localities listed from south to north. LINCOLNSHIRE.-Stoke Rochford, top quarry; coral bed in Ancaster Freestone equivalent, Castle Quarry, Ancaster ; Wilsford Beds, rst and 3rd railway-cuttings east of Ancaster Station; I

Figd. Davidson (1884), PI. XX, Fig. 3, as Rltyncltonella baiineusis Szajnocha,

H . M. M UIR- W o on ,

? Kirton Beds, qu arry ~. mil e E.s.E. of chur ch, S. Car ItO!! ; cr~g­ ball s in Kirton ceme nt-shale , Alpha Cement Co. Qy., K irt on-inLindsey . Specimens are preserved in th e Brit ish Museu m (Nat. Hi st .) and Mr. P. E . Kent' s ColI. DI ME NSIO NS :- Rolotype [BB. 6643J maximum length 7 mm . ; maximum width 8.1 mm . ; maximum thickn ess 5.3 mm . P ar atype, slightl y immature [B .B. 6632J maximum length 5.9 mm. ; maximum width 7 mm. ; maximum th ickness 4.1 mm .

38 FIG.

3~

42. -Pm'virhy " chia kirtonensis sp . nov .

DESCRI PTI ON :- The neanic shell is approximately circular in outl ine, but te n ds to become laterall y elongated . In th e gerontic stage, width and length are again ap proximately equa l. The brachial valve is post eriorly sulcate or flatt ened according to t he amount of in cur vature of the umbo, whil e the ventral umbo is flattened. Both va lves rapidly become conv ex , and a dorsal median fold and ventral sin us are developed abo ut 2 mm . below the umbo. Both fold an d sinus become increasingly dem arcated from the lateral slopes in later growth-st ages. The fold , however .

TWO NEW SPECIES

OF

BRACHIOPODA.

479

tends to remain flattened and the sinus shallow. The linguiform extension of the pedicle valve is about 3.5 mm. in length in the adult shell and tapers dorsally. The umbo is much produced, erect to suberect, and tapers acutely. In well-preserved specimens the circular or elongate-oval foramen is well separated from the dorsal umbo by conjunct deltidial plates which tend to be marginate or auriculate. The beak-ridges are angular and hypothyrid in position. The shell is ornamented by about I I prominent angular costae, about six of which extend to the umbo. The remainder are developed by bifurcation of the costae on the lateral slopes, and the middle costa of the fold is intercalated below the umbo. There are, as a rule, three simple costae on the fold and two in the sinus in the adult. Immature specimens are frequently ornamented by six costae, with two on the fold and one in the sinus. The costae are separated by deep subangular sulci of approximately the same width. Fine growth-lines or prominent growth-lamellae form a transverse ornament. Owing possibly to decortication of the shell the fine radial capillae characteristic of the genus Parvirhynchia were rarely observed. INTERNAL CHARACTERS :-Investigation of the internal structure by grinding longitudinal sections showed that the crura are of the type described as calcarifer (Muir-Wood, 1934, 1936) (Text Fig. T, 4). Transverse sections of specimens which had previously been burnt showed that the internal structure is similar to that of specimens of Parvirhynchia parvula ? (Eud. Desl.) from the garantiana zone of Dorset. The dental lamellae extend across the cavity of the pedicle valve in the posterior transverse sections only. Little callus thickening was observed in either valve showing that P. kirtonensis is not a phylogerontic species. The hinge-plates are not conjunct and are not supported by the median septum which always remains of low elevation. The inner socket-ridges are scarcely demarcated from the hinge-plates which are narrow medio-laterally and inclined at an angle of 45° to the horizontal. The crural bases are given off ventrally. An accessory socket in the outer socket-ridges articulates with the denticula of the pedicle valve, while the hinge-teeth are deeply inserted into the finely crenulated sockets. The median septum seen through the test is 2.5 mm. long in a specimen with a dorsal valve 5.5 mm. in length. The dorsal and ventral adductor scars are obscure. VARIATION :-The chief variation of this species is in the convexity of the shell, in the elevation of the fold, in the depth of the sinus and in the number of costae. A few specimens have IS instead of I I costae, others, although nearly adult, have only 7 costae. Two specimens had four costae on the median fold instead of three, and one specimen from the Wilsford

H. M. MUIR-WOOD,

Coral Bed had five costae in the shallow median sinus instead of the usual two. The Ancaster and Wilsford specimens frequently have a slightly less prominent median fold than the Kirton specimens and the sinus may also be shallower. REMARKS. P. kirtonensis differs from the figure of the type of P. parvula (E. E. Deslongchamps, 1862, p. 276, PI. V, Figs. 5, 6) from the Inferior Oolite of Milly, Sa6ne-et-Loire, by its smaller dimensions, more numerous costae, and by the greater elevation of the median fold which is better demarcated from the lateral slopes in the Lincolnshire species. Deslongchamps' specimen, according to Roche (1939) who has investigated the Inferior Oolite of the Macon district, was obtained from the pre-blagdeni

FIG. 43.-TRANSVERSE SECTIONS OF SPECIMEN OF

kirtonensis sp. nov.

Parvirhynchia

zone. It is doubtful therefore whether it is identical with specimens identified as P. parvula from the Upper Inferior Oolite, Marl Bed, garantiana zone of Bradford Abbas, Dorset, as figured by Davidson (1878, PI. XXVII, Fig. 21) and recorded by Richardson (1930, pp. 57, 58). No French material was available for comparison, but Roche's figures of specimens from the Calcaire a Polypiers, pre-blagdeni zone, indicate a form which is not identical with the Bradford Abbas specimens, but appears to be nearer to specimens from the discites zone of the Cotteswolds. Until the species has been thoroughly studied it is not proposed to separate the British forms for which, however, Buckman's name P. pellucida is already available (Buckman, 1917, p. 229, PI. XVIII, Fig. 28).

TWO "lEW SPECIES OF BRACHIOPODA. The British specimens of P. parvula (= P. pellucida) differ from P. kirtonensis in their larger dimensions, less prominent median fold, and in having less angular costae, some of which tend to become obsolete on the anterior half of the shell, while bifurcation of the costae on the flanks is less frequent. Growthlamellae are only prominent in the umbonal region instead of on the entire shell as in P. kirtonensis, and capillation is more strongly developed in the Bradford Abbas specimens. P. auriculifera (Richardson and Upton) from the Pea Grit, murchisonae zone, and its variant from the scissum zone of the Cotteswolds, is a slightly larger, more convex shell with more numerous costae than P. kirtonensis. An unnamed species of Parvirhynchia from the discites zone of the Cotteswolds resembles P. kirtonensis more closely than any other form examined, and the cost at ion is similar. The Cotteswold specimens are, however, more flattened posteriorly, more convex anteriorly, and the umbo is more incurved than in P. kirtonensis. Genus Zeilleria Bayle r878. Zeilleria wilsfordensis sp. nov. Fig. 44 (r-3 B ) , 45· DIAGNOSIS :-Zeilleriid, approximately circular in outline, about 8.5 mm. long, 8.8 mm. wide, and 4.5 mm. thick; both valves convex posteriorly, flattened anteriorly, anterior commissure plane or incipiently uniplicate, not thickened. Umbo tapering, tubular, suberect to incurved, projecting beyond brachial valve, beak ridges subangular, telate, mesothyrid to permesothyrid in position; deltidial plates disjunct, growthlamellse rare, growth-lines forming fine transverse ornament. Apical angle 80°. TYPE-SPECIMEN :-Rolotype from the Lincolnshire Limestone, Wilsford Beds, third railway-cutting (No. ro), E. of Ancaster, Lines. and preserved in the British Museum (Nat. Rist.) [BB. 3795]. Paratypes from the same locality and horizon and preserved in the same collection [BB. 3798-99] also from the Ancaster Freestone, Newton and Scott's Qy., Ancaster, Lines. [BB. 6644]. MATERIAL AND LOCALITY.-About 30 specimens from the Lincolnshire Limestone, Wilsford Beds; coral-bed in Ancaster Freestone; Castle Bytham coral-bed, etc.; discites or postdiscites zone. Localities listed from south to north. LINCOLNSHIRE.-Castle Bytham coral-bed, quarry about a mile westward of Carlby, near Essendine, ; coral-bed in ' Roadstone,' Castle Lime-works, Castle Bytham; Station Qy., Great

H. M. MUIR-WOOD,

Ponton; Ancaster Freestone, Newton and Scott's Qy., Ancaster; coral-bed in Ancaster Freestone equivalent, Castle Qy. near Ancaster; Wilsford Beds, first, second and third railwaycuttings, east of the station, Ancaster. Specimens are preserved in the British Museum (Nat. Hist.] collections. DIMENSIONS :-Rolotype [BE. 3795J maximum length 8.2 mm.; maximum width 8.8 mm. ; maximum thickness 4.2 mm. Paratype [BB. 6644J', maximum length 9.5 mm.; maximum width o.a mm: maximum thickness Ll2 mm.

FIG.

44.-Zeilleria unisfordcnsis sp. nov.

DESCRIPTION :-In early growth-stages the shell is biconvex, but both valves tend to flatten rapidly in the ephebic stage. No median fold or sinus is developed, and the anterior commissure is plane or slightly arched dorsally. The two valves meet anteriorly at an acute angle and there is no thickening along the commissure. The shell outline is circular in all growth-stages. The umbo when preserved intact is produced, tubular, incurved and almost in contact with the brachial valve in the gerontic stage. In most specimens, however, it is imperfect and appears suberect, with disjunct deltidial plates and an incomplete foramen. The beak-ridges are subangular and mesothyrid or permesotltyrid in position, and the inter-areas are broad and concave. I

From the Ancaster Freetone, Newton and Scott's Qy., Ancastcr.

TWO

NEW SPECIES OF BRACHIOPODA.

The margin of the pedical valve bordering the delthyrium is thickened for the attachment of the teeth, and appears as a narrow smooth rectangular area on each side of the deltidial plates. INTERNAL CHARACTERS :-Transverse sections of specimens which have been previously heated to redness in a bunsen flame, showed that the hinge structure is nearer to that of Z. cornuta (]. de C. Sowerby), the genotype of Zeilleria, than to that of the genotypes of Ornithella or Rugitela. The dental lamellae only extend across the cavity of the pedicle valve for about 0.5 mm. below the apex of the shell. The sockets are deep and narrow and the slender tapering teeth are deeply inserted. Denticula in in the pedicle valve and accessory sockets in the outer socket-

FIG. 45.-TRANSVERSE

SECTIONS OF SPECIMEN OF

wilsfordensis sp nov.

Zeilleria

ridges are not well developed. No cardinal process is developed. The hinge-plates which project ventrally at an angle of 40° to the horizontal are fused with, and scarcely demarcated from the inner socket-ridges, and are separated by a deep flattened septalium. The inner socket-ridges interlock with a sulcus on the teeth and assist in the articulation. The crural bases are given off ventrally and unite with a loop, which extends nearly to the anterior margin of the shell. The cavity of the dorsal valve is infilled with callus posteriorly, an indication of phylogerontism. The dental lamellse seen through the test are 1.8 mm. in length, in a ventral valve 8.5 mm. in length, and diverge from the umbo at an angle of 25°.

H. 1\1. MCIR-WOO]),

The median septum is 4 mm. in length in a brachial valve 8.8 mm. long, and supports the hinge-plates posteriorly. VARIATION :-Comparatively little variation occurs in examples of this species. Some of the specimens have a more convex brachial valve and are slightly more elongate than the type (Fig. 44, 3 B), while a few specimens have an almost flat brachial valve. In two or three examples there was a slight ventral notch of the anterior commissure, suggesting a sulcate trend in later species. Little variation was observed in the size of the adult shell from different localities, and the dimensions given of type and paratype are a fair average for the species. The largest specimen observed was 12 mm. long, II.S mm. wide, and 6.5 mm. thick. This specimen [BB. 4908J was from the coral-bed in ' Roadstone;' Castle Bytham, Lines. REMARKS :-The small dimensions, shell contour, and beak characters readily distinguish Z. wilsjordensis from any previously described species of the British Inferior Oolite. The small biconvex form with subcircular contour described by Buckman as Z. oppeli from the Aalenian of Burton Bradstock, Dorset, is found to have a shorter umbo, differently placed beak-ridges, and to have the internal structure of Cincta. 'Z.' [CinctaJ anglica (Oppel) from the murchisonae zone of Somerset can be similarly distinguished. 'Zeilleria' leckenbyi (Davidson) from the Oolite Marl of the Cotteswolds, is a larger, more pentagonal shell, with a slightly sulcate dorsal valve, more erect and less tubular umbo, conjunct deltidial plates, and different internal structure as shown in transverse sections. Z. cleevensis Richardson and Upton from the Lower Trigonia Grit, dis cites zone of the Cotteswolds is a larger, more convex form, but the shell decreases in convexity anteriorly, and the umbo resembles that of Z. u.'ilsjorde;tsis in being tubular and incurved. The internal structure of Z. eleevensis differs, however, from that of Z. wilsjorde1!sis, and it is probable that the two species are not congeneric. No Zeilleriid comparable with Z. wilsjordensis occurs in the 'Cpper Inferior Oolite. Z. hughesi (Davidson) which, although a larger form, has a superficial resemblance to Z. wilsjordensis, has the internal structure of Rugitela, to which genus it is now assigned. REFERENCES. BAYLE, E. 1878. Explication carte geologique de la France. IV, Atlas I, explan. pIs. viii. ix. Bt:CK~IAN, S. S. 1<)14. Cenera of some Jurassic Brachiopoda, pp. 1-2, London. -'---. H)IS. The Brachiopoda of the Xamyau Beds of Burma; Preliminary Notice. Rec . Geol . Suru, India, xlv, pp. 7S-81.

TWO NEW SPECIES OF BRACHIOPODA.

BUCKMAK, S. S. 1<)17. The Brachiopoda of the Narnyau Beds, Northern Shan States, Burma. Palaiont . Ind. (N.S.), iii, no. 2, pp. 1-299, pIs. i-xxi. DAVIDSON, W. A 'Monograph of British Fossil Brachiopoda (Pala-ont , Soc.). ---1851-1882. Vol. 1. ---1872-1882. Vol. IV Supplement. ---1882-1884. Vol. V Supplement. ELDES-DESLONGCHAMPS, E. 1862. Etudes critiques sur des Brachiopodes nouveaux ou peu connus. Fasc. 1,2. Bull. soc. linn. Normandie, Caen, vii, PI'. 248-2<)6, 1'1. v. :.\ILIR-\VooD, H. M. 1934. On the Internal Structure of some Mesozoic Brachiopoda. Phil. Trans. Roy. Soc., B. cxxiii, no. 5°5, PI'· 5 11--567. ---J()36. A Monograph of the Brachiopoda of the British Great Oolite Series. 1. The Brachiopoda of the Fullers Earth. Mon. Palceont. Soc. for 1935· H1CHARDSON, L. 1930. The Inferior Oolite and contiguous Deposits of the Sherborne District, Dorset. Proc. Cottes, Nat. F. CI., xxiv, pt. J, PI'· 35-85. ---1938. Report of week-end Field Meeting in the Stamford district. Proc. Ceol. Assoc. I, PI'· 2<)-45. Rocmc, P. Il)3<). Aalenien et Bajocien du Maconnais et de quelques regions voisines. Theses Fac. Sci, Umiu. LyOJl., cxxxvii (i), PI" 1-355, 13 pis.

EXPLANATION OF TEXT FIGURES 42-45. FIGURE 42. Paruirhynchi a kirtoncnsis sp. nov. Paratype. Inferior

Oolite, Lincolnshire Limestone, coralliferous masses of limestone in lower part of Kirton cement-shale, Alpha Cement Co. quarry, 1~ miles N. of Kirton-in-Lindsey, Lines, L. Richardson CoIl., Brit. Mus. [BB.6632]. X3~. Dorsal view showing marginate foramen. 2 A-C. Parvirhynchia lcirtonetisis sp. nov. Paratype. Lincolnshire Limestone, \Vilsford Coral-Bed, 1St railway-cutting, E. of Ancaster, Lincs. L. Richardson CoIl., B.M. [BB.3772J. X 31,. 2A. Anterior view; 2B. Dorsal view showing marginate foramen; 2C. Lateral view. 3 A-C. Paruirhynchia l.irtoncnsis sp. nov. Holotype. Locality and horizon as for Fig. 1. L. Richardson CoIl., B.l\I. [BB.6643J. X 3Jr. 3A. Lateral view; 3D. Dorsal view; 3C. Anterior view. 4- Paruirhynchiu parvula) (Eud.-Desl.). Inferior Oolite, garantiaua zone, Marl Bed, Bradford Abbas, Dorset. S. S. Buckman Coll., B.M. [B.6I265J. X 2!. Specimen ground longitudinally to show one ' calcarifer' crus, and one hinge-socket.

I.

FIGUlm 43. Paruirliynchia lririonens is sp. nov. Lincolnshire Limestone, Wilsford Beds, 1St railway-cutting E. of Ancaster. B.M. [BB.3773j. Kine transverse sections through the umbones at distances of o. I to 0.2 mm. apart, showing the highly inclined hinge-plates which are not united posteriorly. );'0 septalium is developed.

X 6.

TWO NEW SPECIES OF BRACHIOPODA.

FIGURE 44. Zeilleria wilsjordensis sp. nov. Paratype. Lincolnshire Limestone, Wilsford Coral-Bed, 3rd railway-cutting E. of Ancaster, Lines. L. Richardson Coli., B.M. [BB.3798]. X 31. Dorsal view of immature specimen. 2 A-C. Zeilleria wilsfordensis sp. nov. Holotype. Locality and horizon as for Fig. 1. L. Richardson Coll., B.M. [BB·3795l X 3!. 2A. Anterior view; zB. Lateral view showing tapering umbo; 2C. Dorsal view showing incomplete foramen and disjunct deltidial plates. 3 A-B. Zeilleria wilsfordensis sp. nov. Paratype. Lincolnshire Limestone, locality, horizon and collection as above. B.M. [BB·37991. X 31. 3A. Lateral view showing imperfect umbo; 3B. Dorsal view showing incomplete foramen, and disjunct deltidial plates. 1.

FIGURE 45. Zeilleria wilsfordensis sp. nov. Lincolnshire Limestone, Wilsford CoralBed, 3rd railway-cutting, E. of Ancaster, Lines. B.M. [BB.3796]. Ten transverse sections through the umbones at distances of 0.1 to 0.3 mrn. apart, showing hinge-plates separated by deep septalium. X 6.