90 TRANSACTIONS OF THE WAGNEK FREE 



whether the fossil described by Tuomey and Holmes is really the Area 

 scalaris of Conrad, or not. That paleontologist was acquainted with the left 

 valve only of his species, nor do the collections of the Academy of Natural 

 Sciences, which embrace the greater number of the specimens either 

 obtained or described by Conrad, show any other portion of that species 

 but the left valve. Inasmuch as one of the more important distinguish- 

 ing characters lies in the opposite valve, it is impossible to say whether 

 the form in question would approximate more nearly the South Carolina 

 fossil or Area scalarina, or, indeed, whether it is the equivalent of either 

 the one or the other. All the valves, which include the figured form, are 

 of comparatively small size, and, as far as mere outline is concerned, 

 more nearly resemble A. scalarina. The posterior ribs, however, as in 

 the South Carolina shell, are narrower than in the Florida fossil, lacking 

 the peculiar flattening of that species, and, reasoning from the fact that 

 the shell was obtained from the same series of deposits which also 

 yielded the South Carolina fossil, it may perhaps be assumed that the 

 two are identical. This is, however, a matter of conjecture. The 

 umbones in Conrad's shell are considerably less prominent than in either 

 the South Carolina or the Florida fossil, and possibly the form never 

 attained a size comparable with that of either of the two other forms. 



Area crassicosta, nov. sp. Fig. 30. . 



Shell subquadrangular; vcntricose, ponderous, ornamented with about 

 twenty coarse, elevated, transversely barred, terete, ribs, which are some- 

 what irregular and crowded on the anterior half of the shell, becoming 

 widely separated and profoundly elevated on the posterior half; beaks 

 nearly anterior, looking forward, separated from each other by a fairly 

 broad interval ; hinge-line almost as long as the greatest length of the 

 shell, pectinated with numerous narrow, nearly vertical teeth; ligamental 

 area narrow, elongated, with about six longitudinal lines, which rise 

 toward the apex of the beak ; interior of the shell coarsely rugated ; base 

 ascending anteriorly, profoundly crenated. 



Length, 2.7 inches ; height, two inches. 



Below Fort Thompson. 



This shell can be readily distinguished by its profoundly elevated 

 and widely separated ribs, being the most coarsely costated Area with 

 which I am acquainted. It closely resembles Area rustica, of Tuomey 

 and Holmes (Pliocene Fossils of South Carolina, p. 39, pi. xv, fig. i), 

 and may, indeed, be that shell. Unfortunately, these authors have given 

 but a very meagre and unsatisfactory description of their species, which 

 barely permits of an absolute determination being made. Their figure, 

 drawn from a mere fragment, does not represent the profound ribs seen 

 in the Florida fossil ; the posterior interspaces are apparently also much 



