part 4] evolution of the liparoceratid.e. 279 



Diameter. 



Whorl height. 



Wli 



orl thickness. 



Umbilicus. 



mm. 



per cent. 





per cent. 



per cent. 



14 



43 





50 



— 



22 



46 





52 



— 



50 



48 





54 



2 7 



120 



48 





56 



30 



Occurrence. — Deeded '/ 'casta sub-zone, Bracebridge and Wad- 

 din gton, near Lincoln (7, p. 104). 



Androgynoceras divaricosta closely resembles specimens found 

 in Dorset which are intermediate between A. lateecosta and A. 

 deed ali cost a, having a round whorl with slightly-flattened sides, 

 tubercles nearly paired, and a moderately-wide umbilicus. The 

 sutures indicate, however, that they belong to different series. 



A. divaricosta has a superficial resemblance to Liparoceras 

 pseudostriatum, from which it may be distinguished by 



(1) Greater arch of the periphery and rounder whorl. 



(2) Suture less complicated and having a large external saddle. 



(3) The tubercles are only just becoming imparinode, and sometimes 



show longitudinal elongation. (Extension of tubercles in Liparo- 

 ceras is usually, but not always, transverse.) 



The' young have a wider umbilicus than the }*oung of sphaerocones 

 of JBecheiceras and Liparoceras. 



D. Amblycoceeas. 



Amblycoceeas brevilobatum, sp. nov. (PI. XXIY, fig. 3 ; 

 text-fig. 10 c, p. 283.) 



Holotype : Liparoceras capricornu Richardson. 1 



Compare Amblycoceras capricorniim Hyatt. 2 



Compare .4. maculatvm Quenstedt, 4, pi. xxxiv. figs. 7-9. 



Dimensions of holotype : — 



Diameter. Whorl height. Whorl thickness. Umbilicus. 



48 mm. 29 per cent. 27 per cent. 44 per cent. 



A Capricorn with elevated whorl and strong ribs, which are not 

 much diminished on the periphery, where they curve forwards. 

 The peripheral rib-curve is generally much less than that of 

 Oistoceras, but often varies in individual specimens ; thus some 

 examples resemble Oistoceras, but are easily distinguishable by 

 their sutural proportions. Sutures moderately complicated; first 

 lateral lobe shallow and narrow, the ventral lobe has a broad 

 median saddle, and the external saddle has three subequal terminal 

 folioles (text-fig. 10 c, p. 283). 



Development. — (Studied in specimens of A. hrevilobatum from 

 the Brick-Pit, Pilley, Leckhampton.) 



The young forms in which the development was studied, had at 



1 L. Richardson, ' Geology of Cheltenham. &c.' 1904, pi. xv, fig. 7. 



2 A. Hyatt, in Eastman-Zittel. ' Text-book of Palaeontology ' 1st ed. vol. i 

 (1900) p. 578, fig. 1204. 



Q. J. G. S. No. 296. z 



