272 BULLETIN OF THE 



'5ENU3 CALLOCARDIA A. Adams. 

 SoBGENus VESICOMYA Dall. 



Shell small, smooth or concentrically striate; hinge of Meiocardia but with- 

 out lateral teeth; epidermis polished, umbones moderately prominent; lunule 

 circumscribed by a groove; otherwise as in Meiocardia. Type Callocardia 

 atlantica Smith (Chall. Rep. Lam., p. 156, pi. vi. fig. 8). 



In his excellent work on the Lamellibranchiates of the Challenger expe- 

 dition, Mr. Edgar A. Smith has pointed out that the dentition of these shells 

 differs from the single valve of Callocardia known, and, while retaining the 

 name, calls attention to similarities with Kelliella. I have carefully studied 

 the hinge of Kelliella, using specimens received from Prof. G. 0. Sars, and also 

 the hinge of C. atlantica and of Pecchiolia subquadrata Jeffreys. They are very 

 difficult objects, owing to their minuteness, shape, and fragility, but I have 

 been able fully to confirm the accuracy of the excellent figure of the hinge of 

 Kelliella given by Professor Sars Jn his Moll. Reg. Arct. Norvegiae (pi. 19, 

 Sg. 15). The hinge of the Callocardia atlantica, if I have rightly identified 

 my little shell, of which I feel pretty confident, is destitute of the angular 

 arrangement noticeable in Kelliella miliaris, and resembles that of Meiocardia, 

 deduction being made of the posterior (and only true ?) lateral tooth existing 

 in that genus and in Bucardium or Isocardia (cor). In the Jeffreys collection 

 I find two lots of specimens labelled Pecchiolia subquadrata. One comprises 

 two small and mutilated valves; the other, three fresh specimens, all of which 

 were obtained by the Porcupine expedition. Judging by these, the figure 

 (P. Z. S., 1881, pi. Ixx. fig. 3) of this species is poor; the shell is usually 

 higher in proportion to its length, more as in Lyonsiella abyssicola Sars. The 

 two largest valves measure 4.0 and 4.0 mm. high against 4.5 and 5.0 mm. 

 long. Only one approximates to the figure, and the cause is evidently patho- 

 logical. Dr. Jeffreys calls attention to the thickness of the hinge-line, com- 

 pared with the size of the shell, and describes it a.« edentulous. This probably 

 arose from the fact that the extremely thin and fragile lamellar teeth snap off 

 even with the hinge-line if the shell be forced open after drying with valves 

 closed, or at most but one tooth remains. 



To get the dentition, which I saw was mutilated in the specimen which 

 seems to have served Dr. Jeffreys for his descrijJtion, I sacrificed the best 

 perfect specimen, breaking away the ventral margins without opening the 

 valves, and in this way found it perfect. When closed the left short cardinal 

 is in front of and above the right short cardinal, and the left long cardinal in 

 front of and below the right-hand equivalent tooth, as in Isocardia. The ex- 

 ternal ligament is visible inside when the valves are closed, for there is a slight 

 gape under its posterior end, but its attachments and position are strictly 

 marginal and external. The yellowish suffusion of the surface is a little more 



