NO. 2.] DESCRIPTION OF THE FOSSILS. 77 



the examination of the young whorls of the above-named species, proved that 

 in the early stages of even closely-allied species, distinguishing features in the 

 formation of the sculpturing and of the lobe-line, furthermore in the propor- 

 tions of growth, may be more accurately observed and determined than appears 

 from the works of Nikitin. 



According to the statements of the contributors to the English Geological 

 Survey 1 only one species of Gadoceras occurs in the "Kellaways Rock" 

 (and Oxford Clay) of England. In the official reports this species is desig- 

 nated Gadoceras modiolare Luid. sp.^ and to it is added Amm. suUmvis 

 Sow. sp.3 as a synonym. The collection of Cadocerates from Wiltshire, now 

 before me, shows that various species occur, differently developed from their 

 early stages. It is also probable that Luidius's "Nautilites modiolaris" from 

 "Kellaway Bridge in Wiltonia" may be found among these forms, but owing 

 to the imperfect description which Luidius gave of his ammonite, it cannot be 

 decided, which of the forms in question should be called by the name he created. 

 The specific name "modiolaris" being moreover, employed by d'Orbigny and 

 Nikitin for two different and easily recognisable species, I consider it better 

 to drop the specific designation "modiolaris Luid." and to go back princip- 

 ally to Sowerby's descriptions for the designation of the English species from 

 the Kellaways Rock and Oxford Clay. 



In the English materials of Cadocerates the following forms may be 

 distinguished : 



1. A species, slender at an early stage, with a narrow umbilicus, closely- 

 encircling whorls, narrow external surface and falciform ribs*. The 

 advanced stage of this form, which, even when full-grown, has a very 

 narrow umbilicus, is shown in the large specimen figured by Sowerby 

 (1. c. PL 54). To this form I confine the name Amm. (Gadoceras) 

 sublcevis Sow. 



2. Young forms with thicker and somewhat convex whorls, and a broader 



1 'The Jurassic Rocks of Britain', yol. I. pp. 277, 279, vol. II. p. 242, vol. V. p. 11, 361. 



3 E. Luidius 'Lithophylacii Britannici Ichnographia'. p. 18, pi. IV. fig. 292. 



3 J. Sowerby, 'Mineral Conchology of Great Britain', vol. I. p. 117, pi. 54. 



* According to Newton's report (E T. Newton and J. J. H. Teall, 1. c. p. 497) young 



forms like these are classed in English museums as a variety of Amm. (Qumstedto- 



ceras) Marice d'Orb- 



