214 < I.YMKM \. SI \H-\.\ MKMA. KT< . 



scarcely have been predicated of the renowned Bohemian anti- 

 developmental i st . 



Gkmu PTERONAUTILUS, Meek. 

 Shell spiral, involute. finally produced, with lateral \vinr-like 



expansions. 



P. SEKHACMIAM s, Gemit/. I'l. '.*. |i>-. 4<.is. Permian. 



Genus CLYMENIA, Miin.t. 



Sliell discoidal. with many but slightly involute whorl> : >epta 

 >iinple or slightly lolied : siphunclc near the inner wall. 



Fifty species. Tpper Silurian. Devonian. AV/-o//r ; \nrth 

 America. 

 C. UNDULATA, Miinst. I'l. 98, Hir. 4U 9. Fichtelgebirge. 



Genus SUBCLYMENIA, d'Orb. 



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

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



One species. Devonian. Emjiantl. 

 S. KVOU TA. d'Orb. PL ( .)8, figs. 500, 501. 



<;<tms TROCOCERAS, Barr. 



Shell depressed, spiral, nautiloid or nearly discoid.-d : whorls 

 free ; septa simple. Very closely related to 

 Forty-four species. U. Silurian. Bohemia. 



NAUTILUS, Bn-.vn. 



Shell involute or discoidal. few-wliorlcd : septa concave, sim- 

 ple ; si ph uncle 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. Lieviirati. Shell smooth. Permian Living. 



'J. Kadiati. Shell t ransvcrscly ribbed. Principally cretaceous. 



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

 and Lower Chalk. India. 



