TRENTON LIMESTONE. 113 



149. 12. LEPTiENA DEFLECTA. 



Pl. XXXI. B. Fig3. 5a,b. 

 Strophomena deflecta. Conrad, Proc. Acad. Nat. Sci. Philadelphia, 1843, Vol. i. p. 332. 



Resupinate, semioval ; dorsal valve slightly concave and elevated towards the beak, 

 deflected at the angles ; ventral valve moderately convex ; cardinal extremities reflected ; 

 cardinal area wide, partially common to both valves ; foramen partially closed ; surface 

 marked by fine equal striae which are crossed by fine elevated concentric lines, giving the 

 striae a crenulated appearance. 



This is a robust, very symmetrical shell, bearing a close analogy to the L. filitexta 

 ( fig. 3 ) , from which, however, it is apparently distinct. The striae are more distinctly 

 crenulated, sharper, and more elevated than in that species ; though for want of a sufficient 

 number of specimens, and a knowledge of the internal structure of the shell, I still feel 

 some hesitation in regard to its distinctive character. A single specimen, only, has been 

 examined, the prominent characters of which are the nearly flat dorsal valve, with elevated 

 beak and sharply crenulated striae. 



Fig. 5 a. Dorsal valve of the specimen. 

 Fig. 5 b. Cardinal area of the same. 



Position and locality. This species occurs at Mineral Point ( Wisconsin) , associated with 

 numerous other well known Trenton species, leaving no doubt of its true geological 

 position.* 



150. 13. LEPT.ENA RECTA. 



Pl. XXXI. B. Figs. 6 a,*. 

 Strophomena recta. Coitbad, Proc. Acad. Nat Sci. Philadelphia, 1843, Vol. i. p. 332. 



Semioval, nearly semicircular, compressed ; cardinal line very straight, extending beyond 

 the width of the shell, and angulated at the extremities ; area narrow, equally common to 

 both valves ; ventral valve scarcely convex, with a slight mesial depression ; dorsal valve 

 flat, elevated towards the beak ; surface marked by strong bifurcating crenulated striae. 



The specimen under examination has perhaps suffered some distortion, but it is remarkable 

 for the nearly equal areas, and the almost entire flatness of both valves. In its anguldted 

 and extended cardinal extremities it resembles the succeeding species ; but that shell is 

 much longer in proportion to its width, and the striae are less sharply crenulated. 



• Mr. CowK AD has kindly placed this and some other western specimens at my disposal, for the purpose of instituting 

 a comparison between the eastern and western species of our lower formations. 



[ PiLiEONTOLOGY.] 15 * ' 



