242 BULLETIN OF THE 
back toward the lower edge of the posterior adductor. On this band between 
the adductors are the gills, two on each side. There are three long filaments 
and several granulations and pigmented dots on the mantle edge near the anal 
orifice. The rest of the edge is nearly smooth. On each side of the anus is 
a prominent whitish lobule, from which a tube seems to pass back over the 
adductor and a shorter one toward or into the anal tube near its orifice. 
Arca lienosa Sar. 
Arca lienosa Say, Am. Conch., LV. pl. xxxvi. fig. 1, 1832. 
One young specimen was dredged in 19 fms., west of Florida. The Fish 
Commission has dredged in deeper water dead valves of this species measuring 
115.0 mm. long., 65.0 mm. high, and 35.0 mm. in diameter (or 70.0 mm. for the 
whole shell). These had about 38 ribs, narrow and sharply grooved on top 
except in the older third where they were entire and uniformly closely trans- 
versely waved. The epidermis is soft, profuse, moderately long, and dark 
brown. The teeth are small, vertical, uniform and close set. The young are 
sometimes sharply auriculate. The anterior outer margin of the area is not 
covered with the black cartilage, which creeps up more and more in the middle 
line, as the shell grows; thus producing a marked difference between young 
and old. 
Arca reticulata CHEmnNITz. 
Arca auriculata Chemnitz, Conch. Cab., VII. p. 193, t. 54, f. 540, 1784; Gmelin, S. N., 
p. 8311, 1788; Dillwyn, Cat., I. p. 237, 1817 ; Lamarck, An. s. Vert., 2d ed., VI. 
p. 475. 
Arca squamosa Lam., An. s. Vert., Ist ed., VI. p. 45, 1819. 
Arca domingensis Lam., l. ¢., p. 40, 1819; E. A. Smith, Chall. Rep., p. 265. 
Arca clathrata Lam., 1. c., p. 46, 1819, fide Deshayes. 
Arca clathrata Defrance, 1816, fide Nyst, Cat. Arc., 1848. 
Arca gradata Broderip & Sowerby, Zodl. Journ., IV. p. 365, 1829. 
2 Arca congenita E. A. Smith, Chall. Rep., p. 265, pl. xvii. figs. 6, 6a. 
Byssoarca divaricata Sowerby, P. Z. S., 1838, p. 18; Reeve, Conch. Icon., pl. xvi. 
fig. 108. 
2 Arca donaciformis Reeve, Conch. Icon., pl. xvi. fig. 104, 1844. 
Dredged at Stations 65 and 66, off Havana, in 80-127 fms. ; at Station 21, off 
Cuba, in 287 fms., dead; at Station 32, in 95 fms., in the Gulf of Mexico, living ; 
and at Station 262, near Grenada, in 92 fms., fine sand, bottom temperature 62°, 
Tt has not been found living from more than 100 fms. This well-known species, 
usually named gradata or domingensis, appears quite variable in outline, espe- 
; cially in the young. Some of my specimens approach so closely to the figure 
of A. congenita that it has suggested the idea that that may be merely an ex- 
