214 f'LYMENlA, SIJBCLYMENIA, KTO. 



scarcely have been pi-edicated of the renowned Bohemian anti- 

 developmentalist. 



Genu.s PTEEONAUTILUS, Meek. 



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

 expansions. 

 P. Seebachianus, Geinitz. PI. 'IS, fig. 41)S. Permian. 



Genus CLYMENIA, Miinst. 



Shell discoidal. with many but slightly involute whods ; se})ta 

 simple or slightly lobed ; siphuncle near the inner wall. 



Fifty species. Upper Silurian. Devonian. Europe; North 

 America. 

 C. UNDULATA, MUnst. PI. 98, fig. 499. Fiehtelgebirge. 



Genus SUBCLYMENIA, dOrb. 



Shell spiral, planorbiform ; sutures of septa sinuous, not angu- 

 lar on the sides, but with a simple dorsal lobe. 



One species. Devonian. England. 

 S. EVOLUTA, d'Orb. PL 98, figs. 500, 501. 



Genus TROCOCERAS, Bair. 



Shell depressed, spiral, nautiloid or nearly discoidal ; whorls 

 free ; septa simple. Yery closely related to Litui(ei<. 

 Fortj'-four species. U. Silurian. Bohonia. 



^. (ienus NAUTILUS, Breyn. 



Shell involute or discoidal, few-whorled ; septa concave, sim- 

 ple ; siphuncle nearly central. 



Outer surface smooth in the recent species, but corrugated in 

 some of the fossil ones. 



Animal placed with its ventral face to the convex (dorsal) wall 

 of the shell. 



Six living, and nearly two hundi'ed fossil species. 



They are divided into the following groups : 



1. Ltevigati. Shell smooth. Permian — Living. 



2. Radiati. Shell transversely ribbed. Principally cretaceous. 



3. Striati. Shell longitudinall}'^ striate. Oolite of Europe, 

 and Lower Chalk, India. 



