LOWER LIAS OF ROBIN HOOD'S BAY 



137 



pi. 94 (holotype, WM 160). No specimens resembling this 

 holotype were found by Bairstow. 

 2. 1A. armiger (Simpson, 1855: 66 (non Ammonites armiger J. deC. 

 Sowerby, 1840)); Howarth, 1962: 107. From Simpson's descrip- 

 tion this was probably an Apoderoceras, but the type specimen is 

 lost and the species is not identifiable. 



Genus HYPERDEROCERAS Spath, 1926 



Remarks. Bairstow found only one poorly preserved example (CA 

 4053) of Hyperderoceras sp. indet. in bed 540.1 (Polymorphus 

 Subzone). This shows parts of inner whorls at 1 5-50 mm diameter that 

 have strong ribs and ventro-lateral tubercles, followed by septate 

 fragments of larger whorls with a quadrate whorl section, where both 

 whorl height and breadth are 50-60 mm. ie. they are not compressed 

 like Epideroceras at this size. Any of the following four Simpson 

 species might have come from this horizon, but the Bairstow specimen 

 is not specifically identifiable: 



1. Hyperderoceras niamillatum (Simpson. 1843: 28 (non Ammo- 

 nites mamillatus Schlotheim, 1813)); Howarth, 1962: 108, pi. 15, 

 fig. 6 (neotype (designated by Howarth, 1962: 108), WM 2102). 



2. H. validum (Simpson, 1855: 39); Blake, 1876: 278, pi. 7, fig. 3 

 (SM-?holotype): Buckman, 1913: pi. 83 (holotype, SM J3275). 



3. H.retusum (Simpson, 1855: 62); Buckman, 1913: pi. 82 (holotype, 

 WM 184). 



4. H.nativum (Simpson. 1855: 68); Buckman, 1913: pi. 84 (holotype, 

 WM931). 



Family PHRICODOCERATIDAE Spath, 1938 

 Genus PHR1CODOCERAS Hyatt, 1900 



Remarks. Species of Phricodoceras show a considerable amount 

 of variation in rib-density, in the development of lateral tubercles, 

 and in overall size of the tubercles. The specimens from Robin 

 Hood's Bay suggest that a sparsely-ribbed species, here identified as 

 P. taylori, occurs in the lower half of the Taylori Subzone, while a 

 more densely-ribbed species, P. cornutum, occurs in the upper half of 

 the subzone. Tubercle strength depends to some extent on preserva- 

 tion, and in any species tubercles are more prominent when the shell 

 is preserved, compared with their appearance on internal moulds. 

 The Robin Hood's Bay specimens are identified below mainly 

 according to their rib-density, but tubercles are accorded some 

 significance when they are especially large. 



Phricodoceras taylori (J. de C. Sowerby, 1826) 



1826 Ammonites taylori J. de C. Sowerby: 23, pi. 514, fig. 1 

 (holotype, lost (originally in Norwich Museum), from Gla- 

 cial Drift. Happisburgh, north Norfolk, perhaps derived 

 from the Yorkshire coast). 



1855 Ammonites quadricornutus Simpson: 71. 



1884 Ammonites quadricornutus Simpson: 106. 



1911 Phricodoceras quadricornutum (Simpson); Buckman: pi. 

 33 (holotype, WM 495 ; possibly from beds 501-517, lower 

 than P. cornutum). 



RANGE: Beds 50 1 .3-524. 1 , Taylori Subzone; 8 specimens. 



Remarks. P. taylori occurs in the lower and middle parts of the 

 Taylori Subzone at Robin Hood's Bay, where the poorly preserved 

 specimens have the widely spaced ribs (12-13 per whorl at 50 mm 

 diameter) that are typical of the species. The holotype of Ammonites 

 | quadricornutus has the same rib-density, and the strength of the 



tubercles is similar to that shown in Sowerby's figure of taylori, even 

 after allowances are made for slightly different modes of preservation. 



Phricodoceras cornutum (Simpson, 1843) PI. 7, fig. 2 



1843 Ammonites cornutus Simpson: 31. 



1 855 Ammonites cornutus Simpson: 7 1 . 



1 884 Ammonites taylori J de C. Sowerby; Simpson: 105 (includ- 

 ing Ammonites cornutus which Simpson now considered to 

 be a synonym). 



1911 Phricodoceras cornutum (Simpson); Buckman: pi. 32 

 (holotype, WM 185). 



1976 Phricodoceras cornutum (Simpson); Schlegelmilch: 152, 

 pi. 28, fig. 1 (WM 185). 



RANGE: Beds 524.3-530.2, Taylori Subzone; 8 specimens. 



Remarks. P. cornutum occurs higher in the Taylori Subzone than P. 

 taylori, and differs from the latter in having more ribs ( 1 7-20 per whorl 

 at 50 mm diameter) and smaller tubercles. 



Phricodoceras nodosum (Quenstedt, 1846) 



1846 Ammonites taylori nodosus Quenstedt: 136, pi. 9, fig. 21 



(holotype, from Wurttemberg, Germany) (non Ammonites 



nodosus, Bruguiere, 1789). 

 1961 Phricodoceras aff. taylori (J. de C. Sowerby); Dean et al.\ 



pi. 68, fig. 5 (BM C. 1 798 1 . probably from bed 520). 

 1980 Phricodoceras nodosum (Quenstedt); Schlatter: 78. pi. 6, 



figs 5. 6 (from Wurttemberg. Germany). 



Range. A single specimen in bed 520.5, Taylori Subzone. 



REMARKS. All the specimens listed above have the same rib-density 

 as P. taylori, but they have much more prominent tubercles. Even on the 

 internal mould the tubercles appear to be genuinely much larger, as can 

 be seen on the specimen figured by Dean et al (\96l), which has both 

 shell and internal mould preserved on different portions of the shell. 



Genus EPIDEROCERAS Spath. 1923 



Remarks. The only examples of Epideroceras found by Bairstow 

 were parts of two specimens in bed 542.4, Polymorphus Subzone. 

 They are fragments of large septate whorls, with compressed whorl 

 sections at 45-60 mm whorl height, a rounded venter, and radial ribs, 

 but no tubercles. They are too fragmentary and poorly preserved to be 

 specifically identified. The following Simpson species might have 

 come from bed 542.4: 



Epideroceras sociale (Simpson, 1855: 39); Blake, 1876: 278, pi. 7. 

 fig. 6 (SM collection); Buckman, 1914: pi. 95 (holotype, WM 68). 



Family POLYMORPHITIDAE Haug, 1887 

 Genus GEMMELLAROCERAS Hyatt, 1900 



Synonyms. Tubellites Buckman, 1924; Leptonotoceras Spath, 

 1925. 



REMARKS. Gemmellaroceras has been divided in two subgenera: 

 Gemmellaroceras s.s., in the Jamesoni Zone and younger beds, in 

 which the first lateral lobe is trifid, and an earlier Raricostatum to basal 

 Jamesoni Zone subgenus G. (Leptonotoceras), in which the first lateral 

 lobes are bifid (Dubar & Mouterde, 1961: 237; Geczy, 1976: 73-75). 

 In Robin Hood's Bay Gemmellaroceras ranges from the top part of the 

 Macdonnelli Subzone up to near the top of the Taylori Subzone. Most 

 specimens belong to the very small species G tubellum (Simpson) (the 

 type species of Tubellites Buckman, 1924), and those specimens that 



