1889.] NATURAL SCIENCES OF PHILADELPHIA. 303 



SPHJERODOMA: A GENUS OF FOSSIL GASTEROPODS. 

 BY CHARLES R. KEYES. 



It lias 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. And it has 

 even been intimated that this genus, as generally understood, may 

 comprise, in reality, several 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 generic-ally identical with those 

 of Soleniseus of Meek and Worthen. The two genera being co-ex- 

 tensive were therefore synonymous. The first of the two terms was. 

 however, pre-occupied and inasmuch as the several other titles, pro- 

 posed 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 Macroehilus the authors of Soleniseus 

 emphasized certain structural features as being distinctive 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 overlooked by most writers. Theassumed 

 absence, in the members of Phillips' genus, of these characters, and 

 their existence in the shells that were under immediate consideration 

 were regarded 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 Soleniseus. Miller 1 subse- 

 quently referred Macrochilus hallan urn Geinitz to this genus. Shortly 

 afterward White- described two congeneric forms from New Mexico 

 and also 3 included several of the Macrochili. More recently some 

 additional species of Macrochilus were transferred to Soleniseus. 



AVith two possible exceptions the described species hereafter 

 enumerated are confined to the Carbonic, the majority occurring in 

 the Coal Measures. Some of the forms are widely distributed 



i Cat. Am. Palse. Foss.,p. 162. 



- Expl. and Sur. w. 100 Merid., Supp., Vol. Ill, p. xxviii. 



3 Geol. Sur. Indiana, 13th Ann. Rept., p. 153, et seq. 



