MEDINAN, NIAGARAN, AND CHESTER FOSSILS 
103 
While not common, as in case of Cyclonema daytonense, speci- 
mens of Cyclonema gyronemoides are widely distributed in the 
Brassfield of Ohio, and form one of its characteristic species. 
Apparently the latter is not a species of Gyronema. In that 
genus there is a distinct umbilicus, though small, and the inner 
margin of the aperture is not reflexed so as to cover this um- 
bilicus. 
Diaphorostoma clintonense (Foerste) 
Platyceras Niagarense var. Clintonense Foerste, Geol. Surv. 
Ohio, Pal. 7, 1893, p. 554, pi. 37a, fig. 8. 
The type of this species was a specimen with a very low, 
closely coiled spire, but with the last half of the last volution 
curving strongly downward. It was found in the ferruginous 
limestone at the top of the Clinton, just under the Onondaga 
shales, near Mifflintown, in Juniata county, Pennsylvania. 
Diaphorostoma daytonense Sp. nov. 
Platyostoma Niagarense Foerste, Bull. Sci. Lab. Denison 
Univ., 1, 1885, p. 97, pi. 13, figs. 3 a; fig. 22 a, b. 
Platyceras (Platyostoma) Niagarense Foerste; Geol. Surv. 
Ohio, Pal. 7, 1893, p. 553, pi. 25, figs. 3 a; figs. 22 a, b. 
The Brassfield form differs from the typical Rochester shale 
form of Diaphorostoma niagarense (Hall) in possessing a lower 
spire, the height of the body whorl is greater, and there is less 
tendency toward the production of broad revolving ridges and 
grooves; it does not attain as large a size, and the transverse 
striae are finer. Only gerontic forms present the large apertures 
represented by figure 22 in the plates cited above. Most speci- 
mens resemble figure 32 on these plates, but with about 2 mm. 
added to the lateral extent of the last volution. Specimens 
resembling figure 3b on these plates are very rare, and represent 
merely aberrant individuals. For these Brassfield forms the 
name Diaphorostoma daytonense is proposed. 
