374 DESCRIPTIONS OF NEW SPECIES OF FOSSILS 



From C. Lordlyi this shell can be distingiiished by being slightly less convex ; 

 by the anterior end of this being nearly semicircular, the curve only ending at the 

 beaks ; while in Lordlyi, from the most prominent part of the anterior end, over 

 the lunular region, the outline is nearly a straight line. In Lordlyi the posterior 

 end, though rounded, is very narrow, here it is unusually broad. Again, at all 

 ages this shell is regularly costate, while in the other, the ribs are smaller, more 

 irregular, and seem rather like somewhat confused lines of growth ; and finally, 

 in this the lunule is bounded by an incised line, while in that it is strongly bor- 

 dered by a thread-like rib. 



From Cytherea planivieta, Guppy, with which it is congeneric, the differences are 

 only those of outline. In that, the lunular region is very slightly concave, but the 

 great difference is in the posterior end. That species is cuneiform posteriorly, 

 while this is broadly rounded. There is a very slight difference in the teeth, but 

 only of specific value. The anterior tooth is placed in a slightly different position, 

 and the cardinals vary a little in the distance they are placed apart. 



CARDIUM, Linn. 

 C. Petitianum, d'Orb., La Sagra, p. 309, PI. 2Y, figs. 50-52. 

 Fossil, Costa Eica. Living on the Cuban coast. 



C. (TRACHYCARDItTM) MURICATUM, Linn., Sjst. Nat., 1123. 



Very common. Living in the West Indies. 



C. (l^vicardium) serratum, L., Syst. Nat., 1123. 

 Not common. Living in the West Indies.. 



C. (fragum) medium, L., Syst. Nat., 1132. 



Half a dozen specimens. Living in the West Indies. 



C. (trachycardium) declive, n. s., PI. 47, fig. Y6. 



Shell elongated, subequilateral, convex; beaks prominent, nearly central; sur- 

 face ornamented by from thirty to thirty-five ribs with narrow interspaces. The 

 top of these ribs are flat and smooth, or marked only by lines of growth, which 

 become more distinct in the interspaces, giving the sides of the ribs a finely serrated 

 appearance. On the posterior side there are a few minute bead-like tubercles be- 

 tween the ribs. The margin slopes almost equally on both sides from the beak 

 to the middle of the shell, the anterior side being but faintly more convex. The 

 crenulations caused by the ribs on the inner margin are obsolete above, and do not 

 become marked except at the base. 



