272 BULLETIN OF THE 
Genus CALLOCARDIA A. Apams. 
Supcenus VESICOMYA Datu. 
Shell small, smooth or concentrically striate; hinge of Meiocardia but with- 
out lateral teeth; epiderm<s polished, umbones moderately prominent; lunule 
circumscribed by a groove; otherwise as in Meiocardia. Type Callocardia 
atlantica Smith (Chall. Rep. Lam., p. 156, pl. 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. O. 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 in his Moll. Reg. Arct. Norvegie (pl. 19, 
fig. 15). The hinge of the Callocardia atlantica, if 1 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 Metocardia, 
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 
T 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, pl. 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 as 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 foreed 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 description, 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 
