MOLLUSCA OF PORTO RICO. 
485 
Genus MERETRIX Lamarck, 1799. 
Shell oval subtriangular, smooth or concentrically ridged, with a well-marked lunule; hinge 
with three cardinals in each valve, with two unequal anterior laterals in the right valve and one 
lateral in the anterior part of the left hinge; ligament external, prominent; pallia! line sinuous. 
Meretrix albida Gmelin. 
Venus albida Gmelin, Syst. Nat., p. 3287,1792. 
Dione albida Reeve, Conch. Icon.,xiv, pi. x, fig. 39,1863. 
Shell nearly elliptical, subinflated, subsolid; umbonal region rather prominent, the beaks turned 
inward and forward; lunule not impressed, but well marked; surface nearly smooth on the earlier 
growth, but becoming finely concentrically ridged on the later growth; anterior end a little narrowed 
and rounded, straight along the line of the lunule; posterior end broadly rounded. Color, externally, 
white, chalky, or somewhat polished; within, milky white; left valve with three radial cardinals, the 
two anterior united above so as to form an inverted V, the single lateral elevated and rounded or 
compressed; posterior cardinal of the right valve bifid, united above to the anterior cardinal; the two 
anterior laterals small; pallial sinus deep. 
Length, 45; height, 35; diameter, 20 mm. 
Mayaguez, Porto Rico, a number of young specimens and valves and one large valve; San Juan 
Harbor, young valves. 
Meretrix aresta, n. sp. Plate 56, figs. 1, 7. 
Shell large, solid, inflated, white or yellowish, very inequilateral, with prominent much incurved 
prosogyrate umbones, rounded in front, arcuate and almost rostrate behind, the base arcuate; lunule 
cordiform, hardly defined by an obsolete impressed line, but there is no defined escutcheon; ligament 
deeply immersed, very little of it visible externally; surface sculptured with fine, somewhat irregular 
concentric sulci in harmony with the incremental lines, but coarser and more excavated, with often a 
few narrow undulations near basal margin; umbonal region somewhat smoother and often appears 
polished by attrition; interior dull white, not polished, with a short anteriorly rounded subtriangular 
pallial sinus; hinge normal, with a subconic left anterior lateral fitting into a pit in the right valve. 
Length, 51; height, 50; diameter, 28 mm.; a larger valve is 58 mm. long. 
Mayaguez Harbor, Porto Rico, at stations 6061 and 6062, in 12 to 30 fathoms, abundant; a single 
young pair off Puerto Real at station 6074. 
Nearest to M. albida , but with a rougher surface, a different outline, and attaining a larger size. 
Meretrix hebraea Lamarck. 
Cytherea hebrsca Lamarck, An. sans Vert., v, p. 568, 1818. 
Oirce hebrsea Reeve, Conch. Icon., xiv, pi. vm, fig. 34, 1863. 
San Juan, Porto Rico (Gundlach). 
Meretrix maculata Linnseus. 
Venus maculata Linnseus, Syst. Nat., ed. x, p. 686, 1758. 
Dione maculata Reeve, Conch. Icon., xv, pi. in, fig. 11, 1863. 
Quebradillas, Porto Rico (Gundlach). >. 
Subgenus Dione Gray, 1847. 
Meretrix circinata Born. 
Venus circinata Born, Test. Mus. Vind., p. 61, pi. iv, fig. 8, 1780. 
Mayaguez, Porto Rico (Gundlach). 
Meretrix dione Linnseus. Plate 56, figs. 3, 10. 
Venus dione Linnaeus, Syst. Nat., ed. x, p. 684, 1758. 
Dione veneris Reeve, Conch. Icon., xv, pi. vi, fig. 24, 1863. 
Shell triangular-ovate, inflated, subsolid, with high, full beaks, which are curved forward over a 
well-impressed lunule; ligament lodged within a decided escutcheon; surface covered with strong, 
reflected, concentric ribs, which are especially high in front and much reduced on the posterior slope; 
on a posterior radial ridge there is a row of long spines which project outward and backward, and 
behind these, on a second fainter ridge, there is another row of smaller spines; left valve with 
three cardinals, the central one heavy and somewhat bifid, with a short, erect anterior lateral; right 
