DALL: MOLLUSCA AND BRACHIOPODA. 415 
Protocardia panamensis Datt, n. sp. 
Plate 18, figure 1. 
Shell small, very pale brown or dirty cream color, equivalve, subequilateral, 
plump, with elevated subprosocoelous beaks and a narrow thin ligament; sculp- 
ture, except on the posterior area, of small, flat, subequal radial ribs with nar- 
rower channelled interspaces crossed by numerous small, equal, and equally spaced 
concentric lamellae which do not rise above the ribs and are confined to the inter- 
spaces ; on the average there are about thirty-three of the ribs with a smooth cordate 
lunular space in front of the beaks; the posterior area begins with a rib bearing 
minute spinules which are usually lost, leaving merely traces of their presence, 
behind this 21-23 similar ribs, narrower and slightly more elevated than those on 
the disk, with wider interspaces crossed by thinner and sharper concentric lamellae 
than on the disk; three or four of these interspaces instead of lamellae have 
minute, widely spaced spinules easily and usually lost, at the rate of about one 
spinule to four lamellae; these rows of spinules are not uniformly distributed on 
different individuals; a broad, smooth swollen fold borders the posterior hinge 
line; hinge normal, strong; interior polished, whitish; margin sharply serrate by 
the sculpture; the posterior area covers about one-fourth of the disk. Lon. 13.5; 
alt. 138.5; diam. 9.0 mm. 
U. 8. S. “ Albatross,” station 3355, Gulf of Panama, in 182 fathoms, mud, 
bottom temperature 54°.1 F. U.S. N. Mus. 122,928. 
A rather simple and uninteresting little species with no particularly salient 
characters. 
Isocardiacea. 
Vesicomyacidae. 
VESICOMYA Dat. 
? Callocardia (A. Adams, 1864) E. A. Smith, Chall. Rep., Lam., 1885, p. 157. 
Vesicomya Dall, Bull. Mus. Comp. Zodl., 1886, 12, p. 272; 1889, 18, p. 439. Type, 
Callocardia (2) atlantica Smith, op. cit., pl. 6, fig. 8. 
Callocardia (subgenus Vesicomya) Dall, Proc. U. S. Nat. Mus., 1895, 17, p. 693; 
1896, 18, p. 17. 
The unusual character of the gill-filaments in this genus, as displayed in 7. 
stearnsii, rendered it necessary to separate it from association with the Isocardi- 
acea, and an investigation into the nomenclature of Callocardia Adams showed that 
the type really belongs to the Veneridae. The subgenus of 1889 was elevated to 
the rank of a genus in 1895 (Trans. Wagner Inst., 3, p. 551) under the name 
of Callocardia, though the true relations of Vesicomya were still regarded as 
doubtful. Finally further study and more material showed the relationship of the 
original Vesicomya and the so-called Callocardia, rendering it necessary to unite 
