78 POMPECKJ. JURASSIC FAUNA OF CAPE FLORA, [norw. poL. exp. 



external side with coarser, less curved ribs. The advanced stage of this 

 form has been illustrated by d'Orbigny^ as Amm. modiolaris. In the 

 aliove-uientioned publications of the English Geological Survey, this form 

 has been delineated as Anim. iiiodiolaris Luid. The full-grown speci- 

 mens of this sjiecies differ from those of Cadoceras sublceve Sow. sp. 

 in having a wider umbilicus, and the whorls being in transverse direc- 

 tion less closely encircling, and hence lower (with a coarser sculpturing 

 in the medium stages of growth). This second species of the English 

 Jura I designate Amm. (Cadoceras) modiolaris d'Orb. 



3. Nikitin^ reports that be has observed Cadoceras Tchefkini d'Orb. sp. 

 from the English Kellaways Rock in English museums. 



4. Yet another form of Cadocerates from the Wiltshire Kellaways Rock — 

 n. sp. indet. — is before me. Up to a diameter of 60 mm. it is charac- 

 terised by remarkably flat whorls, with a narrow umbilicus and close-set 

 fine ribs with a decided flexure forwards. From its outward shape, it 

 should be placed between Cad. sublceve Sow. sp. and Cad. stenolobum 

 (Keys.) Nik. 



The two first-named species are the Western European representatives 

 of two large groups of Cadocerates, which, especially in the Russian Callovien 

 attain a particularly high degree of development. 



Upon Cadoceras sublceve Sow. sp. follow all those forms which are cha- 

 racterised in their earlier stages by a narrow umbilicus and high-mouthed 

 whorls with fine falciform ribs. Even in advanced stages these forms gener- 

 ally have a narrow umbilicus, e. g. : 

 Cadoceras n. sp. indet. (No. 4 on p. 72). 



„ n. sp. indet., a .similar form from the "Ornatenthon" of Suabia. 



„ Seebachi Behr. {Amm. sublaevis v. Seeb.)^ 



„ placenta (Bean, m-s.) Leek. sp. 



„ Tchefkini d'Orb. sp. 



„ Wosnessenski Grew. 



„ stenolobum (Keys.) Nik. 



„ Nanseni n. sp. (see below) 



1 A. d'Orbigny, 'Paleontologie frangaise'. Terr. jur. I. p. 468, pi. 170. 



2 Bulletin de la Soc. Belg. de Geologie etc. vol. III. p. 34. 



8 Different allied forms, yet undescribed, occur in the "Ornatenthon" of north western 

 Germany, as I have seen in the Gottingen Museum. 



