Kathbun.] 248 [December IC, 



Brazil. Respectfully dedicated to Mr. Orestes H. St. John, lately of 

 the Museum of Comparative Zoolopjy at Cambridge, Mass. 



Area (CueuUea ?) Harttii sp. nov. 



Shell of medium si?e, elongate, gibbous, with the height nearly 

 two-thirds the length. Outline of internal mould subovate, the 

 height of the posterior extremity being much greater than that of the 

 anterior. The beaks are situated at a little more than one-third 

 the length from the anterior margin, are yery pi'oniinent and in- 

 cline strongly forward. Hinge nearly as long as the shell. The pos- 

 terior margin extends obliquely downward and slightly backward, 

 rounding strongly toward the ventral margin. The anterior margin 

 leaves the hinge abruptly, at nearly a right angle, and curves rapidly 

 round to the ventral margin, which is slightly rounded and descends 

 moderately in extending backward. 



The valves are very convex and arch strongly from the beaks to 

 the ventral margin. The depth of each valve is more than one-third 

 the height of the shell. The posterior slope commences abruptly 

 along a line extending from just behind the beaks to the lower 

 posterior corner, and descends rapidly to the hinge and posterior 

 margin. This slope is broad, quite concave just back of the beaks, 

 but becomes nearly straight posteriorly. 



The surfoce is marked by small, rounded or subangular, radiating 

 raised lines, which are very fine at the beaks, where they are of 

 about the same width as the interspaces, or narrower, and increase 

 very gradually in size toward the margin, the interspaces there be- 

 ing much the narrower, and even reduced to mere strias. Fine 

 concentric lines cross the shell;, on the upper portion of the shell 

 they are very regular, but near the ventral margin they become more 

 numerous and are crowded together. As they cross the radiating 

 lines they become very prominent, sometimes giving to the latter a 

 beaded appearance. On the posterior slope the radiatiiig lines are 

 minute, thread-like and near together, being separated by very nar- 

 row depressions. These seem to be made even more beaded in ap- 

 pearance by the concentric lines than are the radiating lines on the 

 main portion of the shell, though they are exceedingly fine. The 

 inner margin of the shell is crenulated. 



This shell is quite a thick one, and none of the exterior characters 

 appear in the interior, so that the angular appearance presented 

 by the external moulds is not apparent in the very numerous inter- 

 nal ones. The characters of the interior are quite obscure in all the 



