dall: mollusca and brachiopoda. 415 



Protocardia panamensis Dall, n. Bp. 



Plate 18, figure 1. 



Shell small, very pale browii or dirty cream color, equivalve, subequilateral, 

 plump, with elevated subprosocoelous beaks and a uarrow thiu ligament; sculp- 

 ture, except on the posterior area, of small, flat, subcqual radial ribs with nar- 

 rower cbauuelled 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 

 tlian on the disk ; tliree 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 

 tlie sculpture ; the posterior area covers about one-fourth of the disk. Lou. 13.5 ; 

 alt. 13.5; diam. 9.0 mm. 



U. S. S. " Albatross," station 3355, Gulf of Panama, in 182 fathoms, mud, 

 bottom temperature 54°.l F. U. S. N. Mus. 122,923. 



A rather simple and uninteresting little species with no particularly salient 

 characters. 



Isocardiacea. 



Vesicomyacidae. 



VESICOITIYA Dall. 



1 Callocardia (A. Adams, 1864) E. A. Smith, Chall. Rep., Lam., 1885, p. 157. 

 Vesicomya Dall, Bull. Mus. Conip. Zonl., 1886, 12. p. 272 ; 1889, 18, p. 439. Type, 



Callocardia (?) atlantica Smith, op. cit., pi. 6, fig. 8. 

 Callocardia (subgenus Vesicotwja) Dall, Proc. U. S. Nat. Mub., 1895, 17, p. 693 ; 



1896, 18, p. 17. 



The unusual character of the gill-filaments in this genus, as displayed in V. 

 stearnsii, rendered it necessary to separate it from association with the Isocardi- 

 acea, and an investigation into tlic nomenclature of Callocardia Adams sliowcd that 

 the type really belongs to the Veneridac. 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 rolationsliip of the 

 original Vesicomya and the so-called Callocardia, rendering it necessary to unite 



