56 NAUTILTDiE. 



Hercoceras, Ban-., 1865. 



Etym. — Erkos, a wall, ceras, a horn. 



Distr. — 2 sp. Middle Silurian, Bohemia ; Devonian, Nassau (?). 



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 

 excavated dorsal side of the shell ; sipliuncle ventral, cylindrical, 

 inflated between the chambers, separated from the shell. 



LiTUiTES, Breyn., 1132. 



Etym. — Lituus, a trumpet. 



Syn. — Trocholites, Emmons, 1842. Palgeonautilus and Palseo- 

 clymenia, Remele. 



Distr. — 28 sp. Silurian ; Europe, North America. L. sim- 

 plex, Barr. (xxxi, 9). 



Shell planorbiform, the whorls close or separate ; the last 

 chamber produced in a straight or outwardly curved line ; lat- 

 eral margins of the aperture extended and curved towards the 

 interior of the shell, contracting the aperture into two distinct 

 orifices. 



OPHiDiocERAS, Barrandc, 1861. Etym. — Ophiodes, serpent- 

 shaped, ceras, a horn. Shell with the produced portion MQxy 

 short or wanting. Distr. — 1 sp. Silurian ; Norway, Bohemia. 



STROMBOLiTUiTES, Remele, 1881. Shell commencing as a small 

 spiral, expanding into an obconic form. L. Silurian ; Germany. 

 8. Torelli, Remele (xxix, 90). 



HORTOEus, Montf., 1808. Whorls not in contact. 



DiscocERAS, Barrande, 1861. 



Etym. — Diskos, a quoit, ceras, a horn. 



Distr. — 3 sp. Middle Silurian ; Russia, Germany, Norway. 



Shell planorbiform ; produced portion verj'- short or wanting ; 

 aperture simple, not contracted. 



M. Barrande describes this as a subgenus under his genus 

 Lituunculus; 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- 

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

 scarcely have been predicted of the renowned Bohemian anti- 

 developmentalist. 



Pteronautilus, Meek, 1861. 



Etym. — Pteron, a wing, and Nautilus. 



Distr. — P. Seebachianus, Geinitz (xxxi, 10). Permian. 



Shell spiral, involute, finally produced, with lateral wing-like 

 expansions. 



