dall: mollusca and braciiiopoda. 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, saud, 

 bottom temperature 42° F. U. S. N. Mus. 122,891. Also from station 3418, ofif 

 Acapulco, Mexico, in 660 fathoms, sand, temperature 39° F. U. S. N- Mus. 

 110,559. 



Limopsis diazi Dall, 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. S. S. " Albatross," station 3418, off Acapulco, Mexico, in 660 fathoms, 

 saud, bottom temperature 39° F. U. S. N. Mus. 122,892. 



Arcidae. 



ARCA (Liune) Lamarck. 



Scapliarca Gray. 



BATHYARCA Kobelt. 



Bathyarca Kobelt, Martini-Chemnitz Conch. Cab., zweite ausg., 1891, Mon. 

 Area, p. 214 ; type, Area peetunculoides Scacchi. 



Area (Bathyarca) nucleator Dall, n. sp. 



Plitte IS, flguro 0. 



Shell small, plump, subglobular, equivalve, inequilateral, white, with a dense 

 villous periostracum ; 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 mai^iu which forms a 

 slightly oblique subcirciilar arc, 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 



