74 AMERICAN JOURNAL 



Family DISCINID^E, Gray. 



Discinidce, Gray, Syn. Brit. Mus. i, p. 155, 1840. 

 Orbiculidce, King, Owen, Chenu, and the earlier authors. 



Shell structure permeated with very minute tubuli ; valves 

 inarticulated. Attached to foreign bodies by a peduncle passing 

 through the lower valve. Valves suborbicular, with a subcentral 

 apex. Animal with free spiral arms ; mantle very vascular, 

 fringed with long chitinous setse. 



For synonymy of family, see my report in Bull. Mus. Comp. 

 Zool. vol. iii, No. 1, June, 1871. 



Synopsis of the Family. 



Genus Discina, Lam., 1819. Type D. striata, Schum. 



Subgenus Discina, (sensu stricto). 



Shell with subequal externally convex valves, with subcentral 

 apices. Lower valve with a small subtriangular prominence in 

 the centre, with a minute circular orifice for the pedicel, beneath 

 it, from which an impressed line or furrow extends, on the inside, 

 posteriorly. Shell of rather solid texture, impunctate, perfo- 

 rated by minute tubuli? Type D. striata, Schumacher, 1817, 

 = D. radiosa, Gould, -f- D. JSvansii, Davidson, + D. norvegica, 

 Sowerby, + D. ostreoides, Lam. 



Subgenus Orbiculoidea* D'Orbigny (Schizotreta Kutorga.f 



Shell similar to the last, but with the circular perforation at 

 the posterior instead of the interior end of the furrow, which last 

 is impressed from the outside instead of from the inside, as in 

 Discina. Type Orbiculoidea elliptica, Kutorga, Davidson, In- 

 trod. p. 129, PL ix, f. 253-4-5, 1852. 



Subgenus Discinisca, Dall. (= Discina sp. Auct.) 



Lower value more or less flattened, concave or compressed, 

 upper value more convex ; apices of both subcentral, or sub- 

 posterior. Lower value with a small septum as in Discina, be- 

 hind which is a disk or area impressed from the outside, and 

 traversed by a longitudinal fissure in the median line of the 

 valve, extending from a short distance behind the septum, nearly 

 to the posterior margin of the valve, which is often slightly in- 

 dented behind it. Shell more or less horny in texture, minutely 

 tubulous. Type Discina lamellosa, Brod., Rve. Conch. Icon. 

 PI. i, f. 4, 1862. 



*Comptes Rendus, xxt, p. 269, 1847, August. 

 fVerh. Kais. Min. Ges. 1847. 



