274 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 57. 



In this group the mesial septum and the elevated ridges which sus- 

 tain the adductors in the upper valve are so elevated that they divide 

 the cavity of the valve into three compartments when adult. This 

 characteristic is distinct but less emphatic in the only recent species 

 yet described. 



CRANISCUS JAPONICUS A. Adams. 



Crania japonica A. Adams, Ann. Mag. Nat. Hist., vol. 11, p. 100, 1863. — Davidson, 

 Proc. Zool. Soc. 1871, p. 311, pi. 30, figs. 6, 6a; Mon. Rec. Brach., pt. 3, p. 

 191, pi. 27, figs. 10, 11, 1888. 



Type locality. — Gotto Islands, Japan, in 71 fathoms. 



The septum in this species is short and, except in fully developed 

 specimens, hardly elevated enough to markedly divide the anterior 

 space. Another peculiarity of this species is that the lower valve is 

 subconical and attached to its substratum only by the central apex 

 instead of by its whole surface as in the typical Crania. In one speci- 

 men this attached tip shows a central depression, as if there might 

 have been in the very young a peduncular orifice, but as all the speci- 

 mens were loose valves, dead specimens when dredged, this is doubt- 

 ful. 



Family DISCINIDAE. 



Genus DISCINA Lamarck. 



Discina Lamarck, Hist. Anim. e. Vert., vol. 6, p. 236, 1819. — Dall, Bull. Mus. 



Comp. Zool., vol. 3, pt. 1, p. 39, 1871. — Davidson, Mon. Rec. Brach., pt. 3, 



p. 102, 1888. 

 OrticuZa SowERBY, Min. Conch., vol. 6, p. 4, pi. 506, 1830. Not of Lamarck, 



Systfeme, p. 140, 1801. 



discina striata Schumacher. 



Crania (B) striata Schumacher, Essai, p. 102, pi. 20, figs. 1 a-f, 1817 (not of 



Defrance). No locality cited. 

 Crania radiosa Gould, Moll. U. S. Expl. Exp., p. 465, figs. 480 a-c, 1852. 

 Orbicula norvegica Sowerby, Trans. Linn. Soc, vol. 13, p. 468, pi. 26, fig. 2, 1822. 

 Discina ostreoides Lamarck, An. s. Vert., vol. 6, p. 237, 1819; not of Turton, Dithyra 



Britannica, p. 238, 1822. 

 Orbicula evansii Davidson, Proc. Zool. Soc, 1852, p. 81, pi. 14, figs. 32-34. 



Type locality. — Cape Palmas, West Africa. Gould. 



