210 GASTEROPODS. 



referred to Soleniscus, the fold on the columella presents 

 essentially the same characters, and is generally well disclosed 

 by breaking away the outer lip of the shell slightly. When 

 the exterior wall of the last whorl is entirely removed, the 

 interior features of the columella are still better exhibited and 

 for a much greater distance. 



As generally recognized, the Macrochilus group has a wide 

 range in time, beginning, according to the species described, 

 in the Silurian, and continuing to the present time. Some of 

 the forms have unquestionably been erroneously assigned to 

 the genus. The typical examples are for the most part from 

 the Devonian and Carboniferous, and, although the group pro- 

 bably continued to flourish after the close of the Paleozoic, it 

 is very doubtful whether the majority of the later forms can 

 properly be regarded as congeneric. In Europe the group 

 became greatly expanded during the later Devonian and Car- 

 boniferous, but in America it is almost wholly confined to the 

 latter age the other forms referred to the genus being, with 

 perhaps two or three exceptions, referable to other groups. 



Polyphemopsis of Portlock has commonly been considered 

 synonymous with Macrochilus, but whether it can be regarded 

 as identical with the group as now defined cannot, at present, 

 be satisfactorily determined. Portlock's genus was founded 

 upon such imperfect material as to hardly deserve recognition 

 in any case, and it would probably simplify matters greatly 

 to ignore the term altogether. There appear to be no good 

 grounds for assigning any American gasteropods to Polyphe- 

 mopsis. The species so referred have, in reality, other generic 

 affinities. 



Soleniscus cooperensis (SWALLOW). 



Macrochilus cooperense Swallow, 1863: Trans. St. Louis Aead. Sci., vol. 

 II, p. 100. 



A small species, having the spire occupying about one- 

 half the entire length of the shell, and with very convex volu- 

 tions. 



Horizon and localities Lower Carboniferous, Keokuk 

 limestone : Cooper county. 



