LOWER LIAS OF ROBIN HOOD'S BAY 



135 



Yorkshire specimens had been figured by Wright, 1 880: pi. 28), and 

 there are many Yorkshire examples preserved in iron pyrites, espe- 

 cially in beds 497 and 499, which are also subject to decay, though 

 less readily than the Dorset ones. 



After Spath wrote about the species in 1925, the remaining 

 ammonites in the Sowerbys' collections were obtained by The 

 Natural History Museum in 1935, and amongst them is a medium to 

 large example (BM C. 67323) of Eoderoceras armatum from Robin 

 Hood's Bay, which might even have been one of Sowerby's original 

 syntypes. At 132 mm diameter it is slightly larger than Sowerby's 

 figure of a 117 mm diameter specimen (assuming that his figure is 

 natural size), but it does not differ in any morphological feature from 

 that figure, and the part now missing at the beginning of the final 

 whorl was once present, judging from remaining traces of old glue. 

 There are some patches of pyritic preservation on the inner whorls, 

 which fortunately do not appear to be subject to decay. As a possible 

 original syntype, and a definite topotype, it is a close morphological 

 match with Sowerby's figured specimen and is clearly the best 

 neotype that can now be selected. It presents an unexpected opportun- 

 ity to finally settle the identity of this frequently quoted species. 



The neotype (PI. 5, fig. 9) consists of 6-6'/2 septate whorls up to 

 about 110 mm diameter, followed by a quarter of a whorl of body 

 chamber ending at 1 32 mm diameter. The whorls are very evolute, the 

 whorl section is near-circular and the umbilical wall and edge are 

 evenly rounded. There are many fine indistinct radial ribs between 

 stronger periodic lateral ribs that end in prominent ventro-lateral 

 tubercles. Ribs of moderate strength cross the venter, curving gently 

 forwards, and there are 3-5 such ribs between adjacent ventro-lateral 

 tubercles. There are no umbilical tubercles. 



In Robin Hood's Bay there are a few specimens in the Macdonnelli 

 Subzone, then the species becomes much more common in the 

 Aplanatum Subzone, with 44, 8 and 7 examples collected by Bairstow 

 from beds 497, 498 and 499 respectively. The highest in bed 499 is 0. 1 5 

 m below the top, and only 0.23 m below the top of the Sinemurian. Six 

 specimens were found lower in bed 499 (0. 15-0.37 m above the base), 

 and the best preserved of them is figured in PI. 8, fig. 2; the latter has a 

 phragmocone ending at ca. 68 mm diameter at the position indicated on 

 the figure, then it has a body-chamber 1.125 whorls long ending at a 

 final aperture at ca. 125 mm diameter (the final 0.35 whorls are 

 detached and poorly preserved, and are not figured). There is no 

 overlap between Eoderoceras and Apoderoceras, and the lowest 

 example of the latter genus occurs in bed 501 . 1 just 0.36 m above the 

 highest Eoderoceras. 



Eoderoceras hastatum (Young & Bird, 1828) PI. 6, fig. 3 



1828 Ammonites hastatus Young & Bird: 261, pi. 14, fig. 3. 

 1914 Deroceras hastatum (Young & Bird); Buckman: pis 102A, 



B (?holotype, WM 661, from bed 493.2). 

 1914 Deroceras impavidum Buckman: pi. 104 (holotype, WM 



166; probably from bed 493.2). 



Range. Found only in bed 493.2, Raricostatoides Subzone; 4 

 specimens. 



Remarks. E. hastatum has more depressed whorls and more 

 widely spaced ventro-lateral tubercles than E. armatum which occurs 

 at higher levels. The specimen figured here (PI. 6, fig. 3) is very like 

 the holotype in having striate ribs angled strongly backwards from 

 the umbilical edge, and the almost identical holotype of Buckman's 

 species impavidum probably came from the same bed 493.2. 



Other species of Eoderoceras: 



lE.diversum (Simpson, 1843: 13); Blake, 1876: 282, pi. 8, fig. 3 (SM 

 J34799); Howarth, 1962: 107, pi. 15, fig. 9 (SMJ34799, neotype). 

 The neotype represents a highly evolute, serpenticone species, 

 which might be an Eoderoceras, but no specimens were found by 

 Bairstow. 



Genus PROMICROCERAS Spath, 1925 



Promicroceras planicosta (J. Sowerby, 1814) PI. 5, fig. 3 



1814 Ammonites planicosta J. Sowerby: 167, pi. 73. 



1822 Ammonites aureusYoung & Bird: 248, pi. 13, fig. 6) (type 



specimen lost). 

 71843 Ammonites siphuncularis Simpson: 46. 

 71912 Androgynoceras siphunculare (Simpson); Buckman: pi. 48 



(holotype, WM 485, from beds 451-454). 

 1925a Promicroceras planicosta (J. Sowerby); Spath: 299-302, 



fig. 8f. 

 1925a Promicroceras aureum (Young & Bird); Spath: 301 , fig. 8d 



(BM 17160, possibly from 451). 

 1926ft Promicroceras planicosta (J. Sowerby); Spath: 171, pi. 9, 



figs 1 (BM C.26337), 7 ('neotype', BM C.2235b); both 



from Charmouth, Dorset. 



Range. Beds 446.33-454. 1 , Obtusum and Stellare Subzones; 290 

 specimens. 



Remarks. The current interpretation of Promicroceras planicosta 

 may not be satisfactory. After lengthy discussion, Spath (1925a: 

 299-302) selected as neotype the specimen BM C.2235b (T. Wright 

 Colin, 1887) from Charmouth, Dorset (almost certainly from bed 

 85), even though Sowerby (1814: 167) said that his main specimens 

 came from Marston Magna, and it is highly probable that the original 

 block of specimens that he figured (Sowerby, 1814: pi. 73, now lost) 

 came from the Marston Marble at Marston Magna, Somerset. Spath 

 (1925a: 305) then created a new species, P. marstonense, for the 

 form at Marston Magna, using as holotype a specimen (BM 43914b) 

 from Sowerby's syntypes of P. planicosta. The selection of a 

 Charmouth specimen as neotype of P. planicosta was unfortunate, 

 and may be invalid because there were Marston Magna specimens 

 available amongst the original syntypes. The designation of a Marston 

 Magna specimen as neotype (or lectotype) would have been much 

 more in accordance with Sowerby's original concept of his species. 

 In any case, the forms of Promicroceras at Charmouth and Marston 

 Magna appear to be very close and the two names are probably 



PLATE 6 



Fig. 1 Crucilobiceras densinodulum Buckman. Bed 486.3. CA 3828; the body chamber is exactly one whorl long. 



Fig. 2 Apoderoceras aculeatum (Simpson). Bed 526.5, CA 4031. 



Fig. 3 Eoderoceras hastatum (Young & Bird). Bed 493.2, CA 3895, x 0.6; suture-lines that probably mark the end of the phragmocone are visible exactly 



one whorl before the aperture. 

 Figs 4, 5 Apoderoceras subtriangulare (Young & Bird). 4, bed 520.7, CA 4018; probably a complete adult microconch, with a body chamber exactly one 



whorl long and a slightly contracted final aperture. 5, bed 502, CA3990; the asterisk marks the probable end of the phragmocone. 

 All figures natural size, except Fig. 3. 



