THE CEPHALOPODA. 
179 
Genus. — Sycoceras, Pictet, 1844 Shell short, straight, oviform. Septa trans- 
verse, numerous, simple. Silurian to Devonian. 
Genus. — Phragmoceras, Broderip, 1834; Campulites, in part, Beshayes, 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 Gyroceratid^, Pictet^ 1854. — Shell spiral; septa simple; siphuncle 
external ; aperture large. 
Genus. — Cryptoceras, d^ Orhigny,\'^^l . Shell spiral, discoidal ; vi^horls contiguous, 
embracing. Septa simple, arched, without lobes and sinuosities. Siphuncle dorsal. 
The species are found in the Devonian and Carboniferous formations. 
Ex. C. subhiberculatum, d'Orb. (fig. 29). 
Fig. 29. — Cryptoceras subtuberculatum, d'Orb. Fig. 30. — Gyroceras Eifeilense, d'Orb. Fig. 31. — Gyroceras ornatuni, d'Orb. 
Genus. — Gyroceras, yo?2 iH/eyer, 1829. Ihachv^, 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). 
6^e;22^6'. — Cyrtoceras, Goldfuss, 1833. Campyloceeas and Trigonoceras, 
A'PCoy, 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. Pound in Silurian, Devonian, and Carboniferous formations. 
