Descbiption of New Species of Fossils. 231 



Leperditia (Isochilina) cylindrica n. sj). 

 Plate 8, fig. 12. 

 Cavapace minute, seldom exceeding two-hundred ths of an inch in 

 length, nearly twice as long as wide : valves very convex and cylin- 

 drical, the anterior and posterior ends snbeqiial and strongly rounded ; 

 cardinal line much shorter than the length of the valve ; tubercle 

 obsolete. 



Surface smooth. 



There appears to be no tubercle or prominence of any kind on the 

 surface of this miiuite species, and so far as can be ascertained the 

 valves do not overlap on the basal border, but as they have not been 

 seen in connection, this feature, on so small a species, may easily be 

 overlooked. 



Formation and locality. In the Hudson-river group at Cincinnati. 

 From Mr. C. B. Dyer, and in former collections from Cincinnati. 



Leperditia (Isochilina) i^hnutissima n. s]j. 

 Plate 8, fig. 13. 



Carapace minute, less than two-hundredths 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 pro- 

 minence at the anterior third of the length ; basal margin of valves 

 not ovei'lapping, so far as can be ascertained. 



Formation and locality. In the Hudson-river group at Cincinnati, 

 Ohio. From Mr. C. B. Dyer. 



Beyrichia tumifrons n. sjp. 

 Plate 8, fig. 11. 

 Carapace small, subreniform or semielliptical, dorsal margin 

 straight nearly as long as the 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 backwards in 



