DALL: MOLLUSCA AND BRACHIOPODA. 397 
standing the periostracum is so conspicuously confined to certain lines ; profile 
slightly oblique, nearly orbicular; hinge line straight, with four or five anterior 
and eight posterior teeth; interior of disk bluish white, smooth, with, close to 
the margin, a continuous series of minute tubercles; muscular scars distinct, the 
anterior very small and adjacent to the hinge plate, the other larger and more 
distant. Alt. of shell, 6.5; of beaks above the hinge line, 0.5; diam. 4.0 mm. 
U.S. S. “ Albatross,” station 3360, Gulf of Panama, in 1672 fathoms, sand, 
bottom temperature 42° F. U.S. N. Mus. 122,891. Also from station 3418, off 
Acapulco, Mexico, in 660 fathoms, sand, temperature 39° F. U. 8. N. Mus. 
110,559. 
Limopsis diazi Datt, n. sp. 
Plate 18, figure 7. 
Shell closely resembling in general appearance L. juarezi Dall, but thinner, 
smaller, the hinge with four anterior and four posterior teeth, the cavity of the 
valve deeper and the interior of the disk radiately finely sulcate with subequal, 
rib-like interspaces which reach and feebly crenulate the margin, which bears no 
tubercles. Alt. 4.2; lat. 4.5; diam, 2.5 mm. 
U. 8. S. “Albatross,” station 3418, off Acapulco, Mexico, in 660 fathoms, 
sand, bottom temperature 89° F. U.S. N. Mus. 122,892. 
Arcidae. 
ARCA (Linné) Lamarck. 
Scapharca Gray. 
BATHYARCA Kononm, 
Bathyarca Kobelt, Martini-Chemnitz Conch. Cab., zweite ausg., 1891, Mon. 
Arca, p. 214; type, Arca pectunculoides Scacchi. 
Arca (Bathyarca) nucleator Datt, n. sp. 
Plate 18, flgure 9. 
Shell small, plump, subglobular, equivalve, inequilateral, white, with a dense 
villous petiostracum ; beaks full, prominent, adjacent, overhanging a long narrow 
amphidetic area; anterior part of the straight hinge line shorter than the posterior, 
each making an angle with the beginning of the valve margin which forms a 
slightly oblique subcircular are, the posterior end being more rotund; sculpture 
very finely and subequally reticulate, the radial and concentric raised lines alike 
bearing long, furfuraceous fringes of periostracum; hinge line not quite as long 
