650 GEOLOGY OF OHIO. 



by a narrow and sharply defined prominence lying between the com- 

 pressed beaks of casts of the interior. Posterior adductor scar large, 

 situated in the postero-basal third of the valves; pallial line simple, 

 sharply defined in casts, extending up the anterior side to the umbonaL 

 cavity. 



Only known species, A. miseneri. n. sp. 



This remarkable genus probably is related to Clionychia, but the 

 relation cannot be very close. The hingement seems to be totally differ- 

 ent, and the muscular impression occupies a lower position. The general 

 aspect also is quite different, being much more like that of certain species 

 of Mytilarca. Some may see in the new genus an intermediate type 

 between Clionychia and Mytilarca, but I am fully satisfied that such a 

 view, even considering that A. miseneri is found in the proper horizon 

 for it, would be erroneous. The hinge of Anoptera is of such a nature 

 that I cannot see how it could have been changed to that of Mytilarca. 

 On the other hand, I can readily conceive how the long hinge of Cliony- 

 chia was at first shortened, and then modified by the development of 

 teeth at each end till Mytilarca had been established. As now viewed by 

 me, Anoptera, like Psilonychia, represents a departure from the regular 

 line of Clionychia that became extinct with the close of the Lower Silu- 

 rian. 



Anoptera miseneri, n. sp. 



Plate 50, Figs. 5-9. 



Shell compressed-convex, rather erect, subovate, narrowest above,, 

 the length and height respectively as three is to four and a small frac- 

 tion ; hinge line very short, passing gradually into the posterior 

 margin ; upper half of anterior outline distinctly concave. Beaks 

 compressed, curving mostly forward over a long and laterally well defined 

 lunule; umboaal ridge defined by a distinct furrow in the postero-cardi- 

 nal slope. Surface with strong, unequal, subimbricating lines of growth. 



I am not acquainted with any Lower Silurian shell with which 

 Anoptera miseneri might be confounded. 



The specific name is given for Mr. John Misener of Richmond, Indi- 

 ana, an excellent collector and keen student of the fossils of the Cincin- 

 nati, group. Science is indebted to him for the discovery of a number 

 of entirety new forms as well of instructive specimens of several species 

 that were but little known heretofore. 



Formation and locality : Upper beds of the Cincinnati group, 

 Blanchester, Ohio and Richmond, Indiana. 



Genus CLIONYCHIA, Ulrich. 



Clionychia, Ulrich, 1892, American Geologist, Vol. X, p. 97 ; also Pal. Minn., p. 493. 



(In press.) 



During the present year I succeeded in obtaining two species from 

 the rocks of the Cincinnati group that seem to belong to this genus.. 



