TRENTON LIMESTONE. 113 



149. 12. LEPT.'ENA DEFLECTA. 



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

 Strophcmuna dijlecta. Conbad, Proc. Acad. Nat. Sci. Philadelphia, 1843, Vol. i. p. 332. 



Resupinate, semioval ; dorsal valve sliglitly 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 slriic which are crossed by fine elevated concentric lines, giving the 

 strife 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^NA RECTA. 



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

 Strophmnena recta. Conkad, Proc. Acad. Nat. Sci. Philadelphia, 1S43, 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 stria>. 



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

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

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

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



* Mr. Conrad 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. 



[ PaL/Eontologv.] 15 



