LOWER LIAS OF ROBIN HOOD'S BAY 



129 



was said to be from bed 497 (Getty. 1973:20. 'Tate & Blake's Jamesoni 

 Zone bed 60' ). The former of Getty's specimens is the holotype of P. 

 regustatum (Buckman. 1914). and this seems to be the correct specific 

 name for the less densely ribbed Paltechioceras in beds 496 and 497, 

 because the lectotype of P. aureolum has the same rib density as in P. 

 tardecrescens, of which it might be a senior synonym. 



Family OXYNOTICERATIDAE Hyatt, 1867 

 Genus OXYNOTICERAS Hyatt 1867 



REMARKS. Determination of species of Oxynoticeras in the 

 Simpsoni Subzone presents many problems: Simpson ( 1843, 1855) 

 proposed the specific names simpsoni, limatus, bucki, flavus and 

 lens, and Spath (1925a) proposed the name eboracense, all for 

 specimens from beds 467 or 468 (the type specimens of aliaenum 

 and dejectum, both of Simpson, 1 855, are lost and the names are not 

 usable). The name simpsoni has date and page priority, and is 

 frequently used for these ammonites. However. Spath's eboracense 

 also has a well-preserved type specimen, and if this represents a 

 species different from O. simpsoni, then it differs only by its more 

 compressed whorls up to 40 mm diameter. But the many examples of 

 Oxynoticeras in beds 467 and 468 show a large amount of variation 

 in whorl compression and rib strength on whorls up to 50 mm 

 diameter, and there are no larger ammonites that can be identified as 

 0. 'eboracense ' in having more compressed whorls than O. simpsoni 

 at large sizes. O. bucki (Simpson, 1 843) and O. lens (Simpson, 1855) 

 are clearly the same as O. eboracense, of which they are senior 

 synonyms; O.flavum and O. limatum. both of Simpson, 1843, are 

 smaller and have slightly thicker whorls like those of O. simpsoni. 

 The lectotype of O. collenoti (d'Orbigny. 1844; figured by Fischer, 

 1994: 85, pi. 17, fig. 3) is also very similar to the types of lens and 

 eboracense . 



Larger collections of better preserved specimens will be needed to 

 determine whether these Oxynoticeras can really be divided into 

 more than one species, so in this paper all the specimens in beds 463- 

 472.1 are identified as O. simpsoni. 



Oxynoticeras simpsoni (Simpson, 1843) PI. 4, figs 5, 8 



1843 



1843 



1843 



1843 



71855 



1876 



Ammonites simpsoni Simpson: 37. 



Ammonites limatus Simpson: 41. 



Ammonites bucki Simpson: 42. 



Ammonites flavus Simpson: 43. 



Ammonites lens Simpson: 80. 



Amaltheus simpsoni (Simpson); Blake: 291, pi. 8, fig. 4 



(BMC. 17903). 

 1881/82 Amaltheus simpsoni (Bean); Wright: 392 (1882), pi. 47 



(1881), figs 4, 5 (SM J18231), 6, 7 (SM J18232). 

 1912 Oxynoticeras flavum (Simpson); Buckman: pi. 55 (holotype, 



WM481). 



1912 Oxynoticeras limatum (Simpson); Buckman: pi. 56, fig. 1 



(holotype. WM 480). 

 1912 Aetomoceras simpsoni (Simpson); Buckman: pis 66A, B 



(holotype, WM 813). 

 1920 Oxynoticeras bucki (Simpson); Buckman: pi. 165A 



(holotype, WM 479a). 

 1925« Oxynoticeras eboracense Spath: 108. 1 10. figs d,e( holotype, 



BMC. 18060). 

 1925« Oxynoticeras simpsoni (Simpson); Spath: 110, figs f, g 



(BM 37998). 

 1961 Oxynoticeras simpsoni (Simpson); Deanef al. : pi. 67, fig. 4 



(BMC.17903). 

 71962 Gleviceras lens (Simpson): Howarth: 105, pi. 15. fig. 3 



(holotype, GSM 26405). 

 1976 Oxynoticeras bucki (Simpson); Schlegelmilch: 140, pi. 22, 



fig. 12 (WM 479a). 



RANGE. Beds 463^170, Simpsoni Subzone; 63 specimens. 



REMARKS. All the figured specimens listed in the synonymy above 

 probably came from beds 467 or 468. O. simpsoni is a distinctive 

 species that has a larger umbilicus and thicker whorls than O. 

 oxynotum and similar species. In Robin Hood's Bay it overlaps in 

 stratigraphical range with Eparietites impendens, from which it 

 differs mainly in whorl section: E. impendens has a differentiated 

 ventral keel, flanked by narrow flat areas then angled ventro-lateral 

 shoulders, and a vertical umbilical wall and rounded umbilical edge; 

 in O. simpsoni the venter is either lanceolate or fastigate with no 

 angles at the umbilical shoulders and without a differentiated keel, 

 and the broad umbilical wall typically slopes at a low angle and 

 merges gradually into the side of the whorl. E. impendens has ribs at 

 least on the inner whorls; most O. simpsoni are smooth, though some 

 early examples retain ribs on small inner whorls. 



The lowest O. simpsoni with no ventro-lateral angles at the side of 

 the keel occurs in bed 463, where there are two large examples: one 

 is part of a solid body-chamber ending at about 340 mm diameter; the 

 other is 380 mm diameter and has half a whorl of body-chamber, but 

 is crushed and less well-preserved. A large fragment from bed 

 464.33 is septate up to at least 256 mm diameter. A smaller O. 

 simpsoni from bed 464.32 is figured in PI. 4, fig. 8, which has ribbing 

 on its inner whorl at about 80 mm diameter, and a small specimen 

 from bed 468 is also figured (PI. 4, fig. 5). 



Oxynoticeras oxynotum (Quenstedt, 1843) PI. 4, fig. 4 



1843 Ammonites oxynotus Quenstedt: 161. 



1843 Ammonites polyophyllus Simpson: 39. 



1845 Ammonites oxynotus Quenstedt; Quenstedt: 98, pi. 5, fig. 11 



(holotype). 

 1 884 Ammonites oxynotus Quenstedt; Quenstedt: 1 75, pi. 22, fig. 



29 (holotype). 

 1909 Oxynoticeras podophyllum (Simpson); Buckman: pi. 8 



(holotype, WM 739). 



PLATE 4 



Fig. 1 Eparietites impendens (Young & Bird). Bed 462, CA 3243. 



Fig. 2 Echioceras raricostatoides Vadasz. Bed 489. CA 3393; wholly septate. 



Figs 3, 6 Paltechioceras tardecrescens (Hauer). 3, bed 497. CA 3572. 6, bed 498. CA 3616; probably wholly septate. 



Fig. 4 Oxynoticeras oxynotum (Quenstedt). Bed 481, CA 3716; wholly septate. 



Figs 5, 8 Oxynoticeras simpsoni (Simpson). 5, bed 468, CA 3692: wholly septate. 8. bed 464.32. CA 3652. x 0.8; the outer whorl is part of the body 



chamber. 

 Fig. 7 Gleviceras doris (Reynes). Bed 476, CA 3726, x 0.6. 

 All figures natural size, except Figs 7 and 8. 



