MOLLUSC A OF PORTO RICO. 
473 
shell; it is covered with a thick epidermis, which is thinner above and shows the sculpture in an 
exaggerated way; pallia! line with a wide shallow sinus. Color grayish, whitish, or purplish. 
Length, 9; height, 7; diameter, 5 mm. 
Mayaguez Harbor; San Juan, Porto Rico. 
Section CTJNEOCORBULA Cossmann, 1886. 
Corbula dietziana C. B. Adams. 
Corbula dietziana C. B. Adams, Contr. to Oonch., xir, p. 235, 1852; Dali, Bull. U. S. Nat. Mils., No. 37, p. 7(1, pi. n, tigs. 7 a-r, 1889. 
Shell solid, triangular, distorted, moderately inequivalve at first, afterwards very inequivalve, 
somewhat inequilateral, rounded in front, with a high, sharp, posterior ridge on the left valve that 
ends in a point at the posterior base; in the first stage of growth there are low, wide, concentric ridges, 
with fine radiating riblets in their interstices; the concentric ridges of the second stage of growth are 
finer, and this part of the shell is rayed with whitish and reddish or purplish rays; in the second stage 
the small valve is merely striated; beaks prominent, turned inward and forward; the uinbonal region 
is somewhat flattened; teeth rather strong. 
Length, 13; height, 9; diameter, 5 mm. 
Mayaguez Harbor, Porto Rico, one left valve. 
Corbula swiftiana C. B. Adams. 
Corbula swiftiana C. B. Adams, Contr. to Conch., p. 230, 1852; Dali, Blake Report, i, pi. it, figs. 5 a-r, 1886. 
Shell subsolid to solid, triangular, nearly equilateral, inequivalve; posterior ridge sharp and well 
developed in each valve, ending in a sharp beak at the posterior base; younger shell nearly smooth, 
concentric strife becoming stronger as the shell grows older, and having faint radial riblets; beaks 
rather sharp, prominent; teeth moderately strong. Color whitish. 
Length, 9; height, 7; diameter, 4 mm. 
Mayaguez, Porto Rico, a great number of worn valves; off Puerto Real, one entire specimen, a 
somewhat inflated variety. 
Corbula aequivalvis Philippi. 
CMMl tequMMs Philippi, Arch. furNaturg., n, p. 227, pi. vii, lig. 4, 1836. 
Corbula cubaniana d’Orbigny, Moll. Cabana, ii, p. 283, pi. xxvi, figs. 51-54, 1845. 
Corbula knoxiana C. B. Adams, Dali, Blake Report, i, pi. I, figs. 3, 3 a-r, 1886. 
Shell solid, elongate-triangular, nearly equilateral, with a strong, sharp, posterior ridge, behind 
which the margin is decidedly truncated; in fact it is sunk below the posterior ridge until it almost 
becomes a lunule; beaks curved inward and forward; surface sculptured with strong, rather regular, 
rounded, concentric ridges, that of the posterior slope has finer ridges; tooth of right valve strong 
and curved upward; that of the left bifid. Color whitish. 
Length, 10; height, 7; diameter, 5.5 mm. 
Beach at Mayaguez, Porto Rico, one broken valve. 
Corbula caribaea d’Orbigny. 
Corbula raribxa d’Orbigny, Moll. Cnbana, n, p. 284. pi. xxvxi, figs. 5-8,1845. 
Shell solid and much inflated when fully adult, thinner and subcompressed when immature, 
subtriangular, drawn out into a decided point behind; beaks rather full, curved inward and forward; 
surface sculptured with rather strong, irregular, concentric ridges, those of the lunule-like posterior 
slope finer. In addition there are scattered, very narrow, radiating threads on the surface. On the 
base there is a wide, flattened area where the valves join that is scarcely sculptured; the right valve 
incloses the left, and throughout its posterior portion it projects widely over the left; beak cavities 
deep; teeth rather strong. There is a well-marked posterior sinus. Color whitish. 
Length, 16; height, 10; diameter, 10 mm. 
Mayaguez, Porto Rico, two shells, one immature and one fully adult. 
Family MYACID4L 
Genus SPHENIA Turton, 1822. 
Shell inequivalve, inequilateral, irregular rostrate behind, roughened; right valve a little larger 
than the left, having a single small tooth in front of the resilium pit; muscle impressions large; pallia! 
line feeble. 
