Descriptions oj Heir Genera and Species of Fossils. 13 



This pi'ett>- littie species is [)robabl3' most nearl\' related to C. car- 

 inafns. ^Miller, but the strongly cariniited sides of the volutions and 

 the sharp keel in that species will distinguish them. The strije also 

 are different. 



Formation and locality: the s[)ocimens examined were found in the 

 layer of dark-blue limestone occurring in the Utica shale, and in which 

 the Modiolopsis cincinnatiertsis. Hall and Whitfield, abounds. 



Collectors: TI. E. Dickhaut, E. O. Ulrich. 



Genus MiCRocEKAS (Hall.) 

 MiCKoCERAS MiNUTissiMUM, n. sp. (Plate VII., lig. 8.) 



[Ety. — Mhuitinsimus, very small.] 



Shell exceedingly small, discoid; volutions from two to three, rounded, 

 not embracing, the last one nearly- separate, and increasing moderately 

 in size; umbilicus shallow, about one and a half times as wide as the 

 dorso- ventral diameter of the outer volution at the aperture; aperture 

 rounded, approaching sub-ovate; surface smooth. 



Greatest diameter, 0.02 inch; convexit}' less than 0.01 inch. 



This shell can easih' be separated from 31. inornatus, Hall, the other 

 species of the genus. In that form the volutions increase much more 

 rapidly in size, and are quite angular on the peripher}- and sides, while 

 in the one under consideration they are rounded. Hall's species is also 

 about three times as large. Another difference, which however may 

 not be constant, is, that the shell of J/, inornatus always has a dark- 

 brown or black color; while all the specimens observed of this species 

 are yellowish white. 



Formation and locality: found associated with Cyclora mimifa, C. 

 depressa and M. inornatus, at Hamilton, O., and near the tops of the 

 hills at Cincinnati. 



Collector: E. O. Ulrich. 



Genus Cyclora (Hall). 

 Cyclora depressa, n. sp. (Plate YIL. figs. 9, 9a.) 



[Ety.— Depresmis, depressed.] 



Shell very small, sub-lenticular, about twice as wide as high; spire 

 much depressed; volutions two or three, angular a little below the 

 middle, increasing moderately in size, and with a barely perceptible 

 convexity on the upper side; sutures deeply impressed ; umbilicus large; 

 aperture rhombic oval; surface smooth. 



