102 paleontology of ohio. 



Leperditia (Isochilina) minutissima. 



Plate 4, fig. 4. 



Leperditia (Isochilina) minutissima, Hall ; Descr. New Species of Fossils from the Hud- 

 River Group, etc., p. 7. 

 Leperditia {Isochilina) minutissima, Hall ; 24th Rept. State Cab., p. 231, pi. 8, fig. 13. 



Carapace minute, less than two-hiindreclths of an inch in length, the 

 width being about two-thirds the length, greatest at the anterior third, 

 giving a broadly ovate outline, with a straight cardinal margin of about 

 two-thirds the length of the valve. 



Surface of the valves smooth, rising into an obtusely pointed prom- 

 inence at the anterior third of the length ; basal margins of the valves 

 not overlapping, so far as can be ascertained. 



Formation and locality: In the Hudson River group, at Cincinnati, Ohio. The 

 original specimens were from the collection of Mr. C. B. Dyer. 



Genus BEYRICHIA. 

 Beyrichia tumifrons. 



Plate 4, fig. S. 



Beyrichia tumifrons, Hall ; Descr. New Species of Fossils from the Hudson River Group, 



etc., p. 7. 

 Beyrichia tumifrons, Hall; 24th Rept. State Cab , p. 231, pi. 8, fig. 11. 



Carapace small, sub-reniform or semi-elliptical ; dorsal margin straight, 

 nearly as long as tho entire length of the valve ; anterior and posterior 

 extremities equal in width, or sometimes having the anterior a little 

 wider; extremities sharply rounded; basal margin very broadly rounded. 

 Surface of valves moderately convex, with a deep, narrow, marginal 

 groove on the basal margin, which becomes obsolete on the ends before 

 reaching the dorsal angles, leaving a sharp carinate border. Body of the 

 valve strongly constricted by two deep, oblique sulci, the posterior one 

 originating in the basal groove and extending obliquely backward two- 

 thirds across the valve; the second extends entirely across the valve at 

 about one-third the length from the anterior end, and is strongly curved 

 backward in the middle, so that the anterior portion of the valve forms 

 a rounded area, which is often the most prominent part of the body, 

 though in some specimens the central ridge is equally prominent. 



Surface minutely granulose. Length, six-hundredths of an inch ; 

 width, about three-hundredths. 



