78 
IOWA ACADEMY OP SCIENCES. 
rian some of the shells attained huge proportions, but with the 
general decline of the group the later ones have heretofore 
seemed to rapidly become dwarfed until only small, unimportant 
individuals were recorded after the Devonian. In the Carbon- 
iferous a few dimunitive species have been described, most of 
them but a few inches in length. In the coal measures of the 
Mississippi basin the remains found were of rather rare occur- 
rence, imperfectly preserved and of very small size. Seldom 
did the shells exceed six inches in length and half an inch in 
diameter. 
Of late years, however, some unusually fine material has 
been obtained in the black shales of the lower coal measures in 
the vicinity of Des Moines, Iowa. Several of these shells were 
so large as to excite considerable wonderment. Some were 
over two feet long and one inch in diameter at the larger end. 
These were thought to be giants of their kind and day. But 
these are small, and all the other Carboniferous species are 
mere pigmies by the side of the recently found shell from the 
coal mines of Fansler. The species is 0. fanslerensis, and the 
unique specimen here described was obtained by Mr. M. G. 
Thomas, state mine inspector. 
