CEIHALOPOBA. 



Shell witli the produced portion very short or ■wanting. 



This sub-genus bears the same relation to Lituunculus (the 

 existence of which is supposed) that Opliidioceras does to 

 Lituites. 



Dhtribution, 3 species. Middle Silurian. Eussia, Germany, 

 Norway. 



Hercoceeas, Barrande, 1867. 



Etymology, erJcoSy a wall, and ceras. 



Type, H. mirum, Bar. Middle Silurian, Bohemia. 



Shell usually involute, as in Nautilus, rarely with separated 

 whorls as in Gyroceras, or with a spire as in Trochoceras. Body' 

 chamher with a diaphragm perpendicular to the axis of the shell, 

 the concavity of which is opposed to that of the last septum. 

 This disposition throws the aperture on the convex side of the 

 shell, which is deejDly excavated. Siphunde dorsal, cylindrical, 

 inflated between the chambers, separated from the shell. 



Nautilus suhtuberculatus, Sandberger, from the Devonian of 

 Nassau, may belong to this genus. 



Bathmoceeas, Barrande, 1867. 



Etymology, in allusion to the imbricated arrangement of the 

 partitions. 



Type, B. complexum, Barr. (Orthoceras). 



Shell having the general appearance of Orthoceras. Part of 

 the body-chamber occupied by a series of imbricating plates, 

 which decrease in horizontal extension from below upwards. 

 Biphunde composed of a series of superimposed funnel-shaped 

 tubes, the narrow end directed towards the aperture of the shell. 



Distribution, 2 species. Middle Silurian, Bohemia. 



AULACOCEEAS, Hauor, 1860. 



Etymology, aulax, a furrow, and ceras. 



Type, A. sulcatum, Hauer, Fig. 7. 



Shell straight, like Orthoceras ; corrugated, 

 with two deep lateral furrows; siphon simple, 

 very small, marginal and dorsal, situated 

 between the longitudinal sulci. The test 

 increases rapidly in thickness towards the 

 apex of the shell. 



The genus is a transition form between 

 the Nautilidce a^ndthe JBelejnnitidce. tion of Auiacoceras'^cHi 



Distribution, 4 species. Upper Trias, catum. 



Austria. 



pa 9 



