60 Mr. A. J. Jukes-Browne on a 



seems to be similar in shape and equally oblique (" transverse 

 oblongo-ovata"), but has several important points of difference, 

 being regularly rounded in front and having a nearly straight 

 postero-dorsal slope, while ventrally it is much deeper, so 

 that the ventral border is nearly a complete semicircle; the 

 shell is rather thin, so that the interior surface is undulating, 

 to correspond with the exterior; the pallial sinus is wide and 

 linguiform, passing beyond the middle of the shell ("medium 

 longitudinis superante"). There seem also to be some diffe- 

 rences in the position of the teeth. 



The present species has also some resemblance to the figure 

 of Clementia grayi, Dall, a fossil from the Upper Oligocene 

 of Florida *. This is an oblong shell, described as " convex, 

 rude, concentrically coarsely and irregularly striated," so 

 that the external appearance is similar, but it is less oblique 

 and less elongate, and has a much deeper pallial sinus ; 

 moreover, Dr. Dall states that the cardinal teeth are entire, 

 whereas in all the other species which I have examined the 

 right posterior cardinal is deeply bifid. 



Dr. Dall has also described the single right valve of a 

 shell from the west coast of Mexico under the name of 

 Clementia solida ; but the dentition of this (as figured) f is 

 very unlike that of any other species of Clementia, and if the 

 shell does really belong to that genus, it will not compare 

 with the form under consideration. 



I have not been able to ascertain how the Porto llico shells 

 came into Mr. Billow's possession, but there seems to be no 

 doubt about their being a new species, and, as the obliquity 

 of shape and the forward position of the umbones are such 

 conspicuous features, I propose to give it the specific name 

 of obliqua. The following is a description both in English and 

 Latin : — 



Clementia obliqua, J.-Br. 



Shell rather larger (59 x 44*5 mm.), fairly strong, not thin, 

 oblong-oblique, the umbones being so far forward that a 

 vertical from them cuts off four-fifths of the length ; anterior 

 side attenuated, owing to the upward slope of the ventral 

 margin (as in Pitaria obliquata) ; postero-dorsal slope long 

 and arcuate, posterior side broadly rounded and subtruncate. 



Valves inflated, dull white, coarsely and irregularly con- 

 centrically striated, not undulated, though some of the 



* Trans. Wagner Free. Inst. Sc. Philad. vol. iii. pi. xxxvii. fig. 12 

 (1900). 



t Proc. U.S. Nat. Mus. vol. xxvi. pi. xiv. fig. 4. 



