210 TIIISOA, (iONTOCERAS, ETC. 



Tretoceras, Salter. 



Founded on 0. bisipkonatum, Sowb., from the Caradoc sand- 

 stone (Silurian). Brit., in which the septa are apparently perfo- 

 rated by two siphuneles ; one of which is a deep lateral cavity 

 continuous with the terminal chamber the caA r it t v affecting at 

 least seven of the uppermost septa, if not the whole. 

 T. BTSTPHONATUM, Sowb. PI. 97. fig. 481. Silurian. Wales. 



Thisoa, Montf. 



Shell ovate-elongate, cucumber-shaped ; apparently two siphons 

 running parallel the whole length of the shell, one of which trav- 

 erses a sort of narrow lateral cavity ; there are also a number 

 of false siphons or holes, which do not extend the entire length 

 of the shell. 

 T. SIPHON ALIS, Serres. PI. 104, figs. 571,572. Jurassic. France. 



Gonioceras, Hall. 



Shell flattened, with extremely salient angles ; septa sinuous ; 

 section of shell, an extended ellipse with projecting angles ; 

 siphuncle ventral. 

 G. ANCKPS, Hall. PI. 97, figs. 483, 484. T.. Silurian. 



Colpoceras, Hall. 



This is probably only a siphon of one of the larger species of 

 Orthocerata. 

 ( 1 . VTRGATUM, Hall. PI. 97, fig. 485. L.Silurian. New York. 



Dictyoceras, Eichw. 

 Is probably an Orthoceras covered by a bryo/oan or coral. 



Genus CLINOCERAS, Mascke. 



Shell conical (allied to Loxoc'cra*. McCoy), the siphtmele side 

 *! raiglil. thr others more or less curved; a constriction below 

 the body-chamber. Septal border with an obtuse-angled saddle 

 on the siplmnclc side, with gently rounded lobes and twoslightlv 

 marked lateral saddles. 



('. DKNS. Mascke. PL I0f>. tig. .~>S7. Krratic L. Silurian blocks. 

 Prussia. 



