214 i I.Y.MKNIA. SI KCLYMKMA. KTC. 



scarcely have been predicated of the renowned Bohemian anti- 

 developmentalist. 



Genus PTERONAUTILUS, Mock. 



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

 expansions. 

 P. SEEBACIIIANUS, Geinitz. PL 1)8, fig. 4 ( .s. Permian. 



Genus CLYMENIA, Miinst. 



Shell discoidal, with many but slightly involute whorls ; septa 

 simple or slightly lobed ; siphuncle near the: inner wall. 



Fifty species. Upper Silurian. Devonian, 

 America. 

 ('. i NDULATA, Miinst. PL 98, fig. 4i)9. 



Genus SUBCLYMENIA, .I'Orb. 



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. PI. 1)8, figs. :><)<>. 501. 



Genus TROCOCERAS, Barr. 



Shell depressed, spiral, nautiloid or nearly discoidal : whorls 

 free ; septa simple. Very closely related to Lituitt'v. 

 Forty-four species. U. Silurian. Bohemia. 



Genus NAUTILUS, Breyn. 



Shell involute or discoidal, few-whorl ed ; 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 lace to the convex (dorsal) wall 

 of the shell. 



Six living, and nearly two hundred fossil species. 



They are divided into the following groups: 



1. Ltpvigati. .Shell smooth. Permian Living. 



2. Kadiati. Shell transversely ribbed. Principally cretaceous. 

 :5. Striati. Shell longitudinally striate. Oolite of Europe, 



and Lower Chalk, India. 



