HKRCOCERAS, L1TULTES. ETC. 213 



Genus NOTHOCEEAS, Barr. 



Shell nautiloid, slightly involute ; septa but little curved, not 

 lobed. 



One species. U. Silurian. Bohemia. 

 N. BoHEMiriiM. Ban-. PL 1*7. fig-. 4 <.)(>. 



Genus HERCOCEBAS, Barr. 



Shell generally nautiloid. the whorls sometimes separated, or 

 even turbinate; body-chamber with a diaphragm perpendicular 



to the axis of the shell, the concavity 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, separated from the shell. 



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



Genus LITUITES, Breyn. 



Shell plano.rbiform, 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. 



Twenty-eight species. Silurian. Europe ; North, America. 

 L. SIMPLEX, Barr. PL 98, fig. 4 ( ,)7. 



Subgenus Ophidioceras, Barrande. 



Shell with the produced portion very short or wanting. 

 Seven species. Silurian. Norway ; Bohemia. 



Genus DISCOCERAS, Barrande. 



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- 

 ti/t.culus; 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 Disooceras ma\ r 

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

 ites ! This is filling up the " gaps " with a vengeance, and could 



