Eathbun.] 246 [December 16, 



portion of tlie sbell is a little higher, than the posterior and is well 

 rounded. The postei'ior margin rounds rather abruptly, and the an- 

 terior more gradually, downward from the hinge toward the ventral 

 margin, which last is moderately curved. The shell is slightly angu- 

 lar posteriorly, where the line of the hinge bends rapidly downward, 

 at a point a little above the median line. 



The surfoce arches quite strongly from the beaks to the ventral 

 margin. The curvature of the surface from the anterior margin to 

 the posterior is more moderate and quite regular. Hinge teeth mi- 

 nute and numerous. The surface is marked by very numerous, regu- 

 lar, fine, thread-like concentric lines, which are very prominent and 

 are separated by slightly narrower interspaces. On one specimen 

 there were about 25 or more of these lines. Length of shell, 8 mm.; 

 height, 5 mm.; depth of each valve, 2 mm. The shell from which 

 these measurements were taken is somewhat above the ordinary size. 

 This form is distinguished from Leda hraziliensis, the next one to be 

 described, by its greater proportionate height and convexity. 



From the cretaceous beds at Maria Farlnha and Pt. Nova Cruz, 

 Prov. of Pernambuco, Brazil, where it is moderately abundant. 

 Dedicated, at Mr. Derby's request, to Mr. II. H. Swift, formerly U. 

 S. Consul at Pernambuco, as a grateful acknowledgement of many 

 favorsi received from him during the trip. 



Leda braziliensis sp. nov. 



Shell very small, moderately convex and elongate, with the length 

 a little greater than twice the height. Beaks slightly anterior to the 

 middle. The hinge, posterior to the beaks, forms a slight inward 

 curve and descends gradually in extending backward. The margin 

 posteriorly forms an acute angle with the hinge, or the shell may have 

 been slightly rounded at this point. The ventral margin forms a 

 lone, very moderate curve, which is somewhat stronger anteriorly. 

 The anterior extremity of the shell is higher than the posterior, and 

 is well rounded. The hinge margin in front of the beaks is nearly 

 straight, or has a slight outward curvature. 



The convexity of the valves is moderate and greatest near the 

 middle. The curve across the valves increases very slightly in 

 strength from the ventral margin toward the beaks, which are minute 

 and pointed. No external moulds have been found. The teeth are 

 very small and numerous. Size : length, 7.5 mm.; height, 3 mm. 



This form of Leda has a shape quite common among the species of 

 that genus ; yet it seems to dilfer enough from all the species with 



