328 
Aug .F. Foerste 
anterior slopes of the shell there frequently is evidence of the inter- 
calation of one or two additional plications. 
35. Anomalodonta costata, Meek 
{Plate IV, Fig. 3) 
1873. Amhonychia costata Meek, Geol. Surv. Ohio, Pal., 1, p. 130, Plate 12, Figs. 
5, a, h, c 
The type of Anomalodonta costata is numbered 790 in the James 
collection at Chicago University. It posseses 19 simple radiating 
plications but the original number may have equalled 24. Compared 
with Anomalodonta alata, the radiating plications are distinctly 
narrower and are separated by relatively broader interspaces, which 
on account of their considerable width appear comparatively flat. 
Anomalodonta costata is a smaller species, usually not exceeding 50 
mm. in height. The concave curvature of the anterior margin and the 
sinuous curvature of the posterior margin are both less, and the 
latter can scarcely be said to be alate; both of these features are 
possessed also by Anomalodonta alata during its younger stages. 
The posterior margin of Anomalodonta costata rarely is well pre- 
served but its direction is indicated frequently by the direction of 
the concentric striae upon such parts of the shell as remain. The 
type is labelled as coming from Cincinnati, Ohio, but the horizon 
of the species is known to extend from the Arnheim, where frequently 
it is common, into the Waynesville member of the Richmond. As 
in the case of Anomalodonta alata, one or two additional plications 
are intercalated occasionally along the hinge-line or on the anterior 
slope of the shell. The total number of plications may reach 27 
or 28. 
36. Byssonychia robusta, Miller 
{Plate IV, Figs 1, A, B, C) , 
1881. Amhonychia robusta Miller, Jour. Cincinnati Soc. Nat. Hist., 3, p. 315, ^ 
Plate 8, Figs. 3, 3a 
1893. Byssonychia richmondensis Ulrich, Geol. Surv. Ohio, 7, p. 632, Plate k-5. Figs. \ 
3, U I 
The types of Byssonychia robusta are numbered 8816 in the 
Faber collection at Chicago University. They are described as 
coming from near Osgood, in Indiana, but are labelled as coming j 
from Versailles, Indiana. At both localities, and at numerous in- j 
