FIEUrorEHAS, MTl ITES. RTC. 213 



(ienus NOTHOCERAS, Karr. 



Slu'll iKiiililoid. slightly involute; septa hut little curxcd, not 

 l()l)e(l. 



One si)ecies. U. Silurian. Bohemia. 

 N. BoHEMicuM, Bair. PI. '.IT, fig. 4;)(). 



(i^nns HERCOCEEAS, Barr. 



Shell generally nantiloid, the whorls sometimes separated, or 

 even turbinate ; body-chamber with a diaphragm perpendicular 

 to the axis of the shell, the concavit}" of which is opposed to 

 that of the last septum, throwing the aperture on the deeply ex- 

 cavated dorsal side of the shell ; siphuncle dorsal, cylindrical, 

 inflated between the chambers, sejjarated from the shell. 



Two species. Middle Silurian. Bohemia; Devonian. Nassau (?). 



(ienus LITUITES, Breyu. 



Shell planorbiform, the whorls close or separate ; the last 

 chamber produced in a straight or outwardly curved line ; lateral 

 margins of the aperture extended and curved towards the inte- 

 rior of the shell, contracting the aperture into two distinct 

 orifices. 



Twent3'-eight species. Silurian. Europe : North America. 

 L. SIMPLEX, Barr. PI. '.18, fig. 41)7. 



Subgenus OpMdioceras, Banaude. 



Shell with the produced portion very short or wanting. 

 Seven species. Silurian. Norioay ; Bohemia. 



Genus DISCOCERAS, Banande. 



Shell planorbiform ; produced portion very short or wanting ; 

 aperture simple, not contracted. 



Three species. Middle Silurian. Russia ; Germany ; Norway. 



M. Barrande describes this as a subgenus under his genus Litu- 

 unculus ; of which no species have been observed, but which 

 he creates by anticipation with the diagnosis : " Shell like Litu- 

 ites^ but with a simple aperture," in order that Discoceras may 

 hold the same relationship to it that Ophidioceras does to Litu- 

 if.es I This is filling up the " gaps " with a vengeance, and could 



