656 GEOLOGY OF OHIO. 



cate) in the upper half and well rounded in the lower, at other times 

 more uniformly curved; base broadly rounded, ascending anteriorly; 

 anterior end very short and small, regularly curved, Beaks very small, 

 scarcely distinguishable, situated far in front; no distinct umbonal ridge; 

 mesial sulcus comparatively deep in the umbonal half, not sharply 

 defined however anywhere. 



Anterior muscular scar very faint, prominent, occupying about half 

 of the small anterior end; pallial Hue moderately distinct, submarginal 

 posterior scar very faint. Back of cast deeply channeled, indicating 

 either a strong hinge plate or an escutcheon in the shell, the former most 

 likely. Cardinal teeth were present but they are not shown clearly 

 enough in casts to be described. Surface of casts with a few distant 

 lines of growth. 



This species is closely related to the Modiolopsis truncata, Hall, but 

 may be distinguished by its more nearly oval outline, and deeper mesial 

 or umbonal sulcus. In the outline it is more like the type of the genus 

 M. oviformis but the casts of that species are not channelled dorsally in 

 any degree comparable with M. subovalis. 



Respecting the generic position of the species, I see nothing to 

 oppose an arrangement with Modiolodon. The same applies also to 

 Modiolopsis truncata, because it is unquestionably congeneric with M. sub- 

 ovalis. Until the latter was discovered and studied I found Hall's species 

 {truncata) most troublesome to classify, and for a time I was inclined to 

 place it into the new genus Eurymya, founded upon Modiolopsis plana, Hall. 



Formation and locality : Upper beds of the Cincinnati group, Ver- 

 sailles, Indiana. Five specimens. 



Genus ACTINOMYA, Ulrich. 

 (Final Rep. Geol. Sur. Minn., Vol. Ill, p. 513 (In press.) 



The type of this genus is the Modiolopsis cincinnatiensis, Hall and 

 Whitfield, described in the second paleontological report of this survey. 

 It is a common and highly characteristic fossil of the lower fifty feet of 

 the Cincinnati group. The figures given by the authors of the species 

 on plate II of the work cited, do not, according to my observation, cor- 

 rectly represent the species. During the past eighteen years I have had 

 opportunities to examine an aggregate of several hundred specimens, 

 most of them in an unusually good state of preservation, and all of them 

 bearing evidence for the great constancy of the specific characters of the 

 form. None, so far as I can remember, could be said to approach even 

 the figures given by Hall and Whitfield in the angularity of the posterior 

 extremity. 



Figure 16 on plate 5t> of this report, represents a well preserved 

 cast of the interior of a large right valve. It shows beside the normal 

 form of the shell, the merely outlined anterior muscular scar, obscure 



