THE CEPHALOPODA. 



179 



Qenus. — Stcoceras, Pictet, 1844 Shell short, straight, oviform. Septa trans- 

 verse, numerous, simple. Silurian to Devonian. 



Qenus. — Phragmoceras, Broderip, 1834; Campulites, in part, BesJiayes, 1830; 

 Phragmolithes, Conrad, 1838. Shell compressed laterally, conical, regularly bent 

 in its length, but not spiral. Septa simple, transverse. Siphuncle very large, subcentral, 

 near the internal margin. The outer chamber large, expanded, terminated by a longi- 

 tudinal aperture contracted into a fissure, the posterior extremity of which is dilated 

 into a large transverse sinus ; and the anterior extremity is prolonged into a smaller 

 subcircular sinus, forming a tube. Upper Silurian and Devonian. 



7. Family GrROCERATiDiE, Pzc^e^, 1854. — Shell spiral; septa simple; siphuncle 

 external ; aperture large. 



Genus. — Cryptoceras, d'Orhigny, 1847. Shell spiral, discoidal ; whorls contiguous, 

 embracing. Septa simple, arched, without lobes and sinuosities. Siphuncle dorsal. 

 The species are found in the Devonian and Carboniferous formations. 



Ex. C. snbtuberculatum, d'Orb. (fig. 29). 



Fig. 29. — Cryptoceras snbtuberculatum, d'Orb. Fig. 30. — Gyroceras Elfeilense, d'Orb. Fig. 31. — Gyroceras omatum, d'Orb. 



Genus. — Gyroceras, uowil/ej^er, 1829. Is xcbvs, Hisinyer, 1837. Shell multilocular, 

 discoidal, with a regular spire, composed of non- contiguous whorls, rolled on the same 

 plane. Septa regular, with simple and symmetrical margins ; the last chamber very 

 large, occupying a third of the last whorl. Siphuncle thin, subdorsal. Aperture oval or 

 angular. Gyroceras is to the Nautilus what Crioceras is to the Ammonite. Upper 

 Silurian and Devonian. Ex. G. ornatum, d'Orb. (fig. 31). 



Ge«ws. — Cyrtoceras, Goldfuss, 1833. Campylocekas and Trigonoceras, 

 liPCoy, 1844. Shell multilocular, not spiral, representing an oblique horn more 

 or less bent. Septa transverse, oblique, with simple borders. Aperture in general 

 oval and compressed. Siphuncle continuous, often dorsal; the last chamber much 

 larger than the others. Found in Silurian, Devonian, and Carboniferous formations. 



