1902.] NATURAL SCIENCES OF PHILADELPHIA. 711 



It attains a height of 35, a length of 39, and a diameter of 

 16 mm. The animal is viviparous and incubates an enormous 

 number of young shells until the adult sculpture is fairly initiated. 

 The brood is fully ripe in August in the Arctic Sea, and about June 

 1 in the Aleutian Islands. The variability of the shell is chiefly in 

 outline, some specimens being longer than others. 



Venericardia (Cyclooardia) rudis Gray, 1839. 



Off the Sea Horse Islands, between Point Barrow and Icy Cape, 

 in 23 fathoms, E. E. Smith; south through Bering Strait and Sea, 

 among the Aleutian Islands, and eastAvard to Kadiak, in 10 to 60 

 fathoms, bottom temperature 35° to 45° F., Dall. 



Shell squarish, compressed, with high, almost posterior beaks; 

 the lunular region deeply indented ; the hinge broad and massive ; 

 the interior white or more or less tinted with livid purple ; sculpture 

 of 12-16 low radial ribs, distally obsolete, with narrower shallow 

 interspaces, with no granulations, covered by a smooth horny brown 

 periostracum, often rude and eroded; height 29, length 31, diame- 

 ter 16 mm. 



Gray, in his description of the shells of Beechey's voyage to the 

 Pacific and Bering Strait, cites Arcturus rudis Humphrey, MS., 

 as a synonym of the Pacific shells which he identifies with Cardita 

 borealis Conrad. As this is the only name associated with the 

 Bering Strait shells except horealis, and it is evident that Gray 

 recognized only one species among them, I have revived the name 

 for the ruder form of the two known to inhabit that region. In 

 well-developed specimens the hinge plate is relatively almost as 

 broad and heavy as in V. planicosta Lam. It is easily distin- 

 guished from V. alashana by the fewer ribs, smooth periostracum, 

 and prominent beaks with the resulting broad hinge plate. 



Venericardia (Miodon) prolongatus Carpenter, 1864. 



Middleton Island, Alaska, in Lat. 59° 35' N., in 12 fathoms, 

 gravel, and south to ISTeeah Bay at the entrance to the Straits of 

 Fuca. 



A small, elevated shell, of pale gray color, and very much the 

 sculpture of V. incisa. It is notable for its prominent beaks and 

 oblique form and was figured in the Proc. U. S. Nat. Mus. , XIII, 

 PI. XVI, figs. 7 and 9, in 1890. Like the other species, it is 

 viviparous. 



