208 GASTEROPODS. 



Genus Soleniscus MEEK & WORTHEN. 



It has long been known that under Macrochilus of Phillips 

 there have been described a number of gasteropodous shells, 

 which differ very essentially from the typical forms of the 

 genus. It has even been intimated that this genus, as gen- 

 erally understood, may comprise, in reality, teveral more or 

 less well-marked divisions of perhaps more than subgeneric 

 value. In a recent note the differences between the various 

 groups were briefly considered, and two well-defined sections 

 made out. At the same time, it was shown that the typical 

 forms of Phillips' genus were generically identical with those 

 of Soleniscus of Meek and Worthen. The two genera, being 

 co-extensive, were therefore 8} nonymous. The first of the two 

 terms was, however, preoccupied, and inasmuch as the several 

 other titles proposed at various times for shells of the same 

 group were unavailable, the generic term suggested by Meek 

 and Worthen must necessarily be substituted. 



In separating the genus from Macrochilus, the authors of 

 Soleniscus emphasized certain structural features as being dis 

 tinctive in their group, but these characters are now known to 

 be present in the typical species of the genus first established. 

 On account of being more or less obscured by the adhering 

 matrix, the peculiarities in question appear to have been over- 

 looked by most writers. The assumed absence, in the members 

 of Phillips' genus, of these characters, and their existence in 

 the shells that were under immediate consideration, were re- 

 garded as sufficiently good reasons for the generic separation 

 of the two groups, and for the establishment of a new genus. 

 A single species only was originally assigned to Soleniscus. 

 Miller subsequently referred Macrocliilis hallianum Geinitz to 

 this genus. Shortly afterward, White described two congen- 

 eric forms from New Mexico, and also included several of the 

 Macrochili. More recently, some additional species of Macro- 

 chilus were transferred to Soleniscus. 



With two possible exceptions, the described species from 

 America are confined to the Carboniferous, the majority occcur- 



