CLASS PELECYPODA 
123 
elevated, recurved; in the left valve elongated, subhorizontal; cartilage 
narrow. 
Type. Axinopsis orbiculatus Sars. 
Distribution. North Atlantic and north Pacific oceans. 
Axinopsis viridis Dali, 1901. 
Proc. U. S. N. M., 23:819; pi. 42, fig. 3. 
Shell small, polished, suborbicular, when fresh covered with a glisten¬ 
ing pale-green periostracum, sometimes exhibiting lighter and darker 
concentric zones; sculpture solely of fine concentric lines of growth; 
beaks low, inconspicuous; lunule slightly impressed, but without any 
bounding sulcus or ridge, small, sublanceolate; escutcheon hardly recog¬ 
nizable, very narrow, and inconspicuous; the part of the lunule belonging 
to the right valve is slightly larger than the other. The ligament is small 
and very delicate, but not wholly concealed. The subumbonal tooth of 
the right valve is prominent and strong, the inflected tooth-like process of 
the left valve is well developed. Margins of the valves smooth, interior 
polished, with some obscure radial striae; muscular and pallial impressions 
normal. Length, 6.2; height, 6; diameter, 3.3 mm. (Dali.) 
Type in U. S. N. M., No. 214743. Type locality, Plover Bay, Bering 
Strait. 
Range. Arctic Ocean and east Aleutian Islands to the Coronado 
Islands, Lower California. Also Japan. 
Axinopsis sericatus Carpenter, 1864. 
Plate 4, fig. 4. 
Suppl. Rep. Brit., Assoc., p. 643. Proc. U. S. N. M., 23; pi. 40, fig. 2. 
Shell small, circular, flat; epidermis silken. (Carpenter.) 
Type locality, Catalina Island, California. 
Range. Aleutian Islands to Catalina Island. 
Family DIPLODONTID2E. 
Genus DIPLODONTA Brown, 1831. 
Shell suborbicular, smooth; ligament double, rather long, submarginal; 
hinge teeth 2.2, of which the anterior in the left valve, and posterior in 
the right are bifid; muscular impressions polished, anterior elongated. 
(Tryon. S. S. Conch.) 
Type. Venus lupinus Brocchi. 
Distribution. West Indies, Rio de Janeiro, Britain, Mediterranean, 
Red Sea, West Africa, India, Korea, Australia, California. 
Range in time. Cretaceous, Pleistocene. 
