MOLLUSCA OF PORTO RICO. 
487 
Mysia tenuis Recluz. 
Dosinia (Artemis) tenuis Recluz., Journ.de Conchyl., in, p. 250, pi. x, fig. 1,1853. 
Shell nearly orbicular, thin to subsolid, subinflated; beaks pointed and turned slightly forward 
over a faint lunule; ligament nearly immersed; surface finely and irregularly concentrically striate, 
whitish; left valve with three diverging cardinals, the anterior with a deep pit in front of it, sometimes 
slightly bifid; right valve with three divergent cardinals, the posterior bifid; hinge plate wide and flat- 
tened behind when the shell is adult; beak cavities deep; anterior muscle scars elongated; posterior 
scars oval; pallial sinus triangular. 
Length, 42; height, 41; diameter, 21 mm. 
Playa de Ponce, Porto Rico, one dead, badly discolored specimen; Mayaguez, one left valve. 
Subfamily CIRCIN®. 
Genus CIRCE Schumacher, 1817. 
Shell subtriangular or subcircular, compressed or slightly inflated, with concentric and sometimes 
radial sculpture; beaks pointed; lunule lanceolate; ligament immersed; hinge teeth like those of 
Meretrix; pallial line entire or showing a slight indication of a sinus. 
Subgenus Gouldia C. B. Adams, 1847. 
Shell small, subinflated, the surface wholly or distally reticulate. 
Circe cerina C. B. Adams. 
Thetis cerina C. B. Adams, Proc.. Bost. Soc. Nat. Hist., Jan., 1845, p. 9. 
Gouldia cerina C. B. Adams, Cat. Coll., p. 29, 1847; Dali, Bull. Mus. Comp. Zool., ix, p. 130, 1881 ; Dali, Blake Report, I, p. 263, pi. 
VII, figs. 4n, 45, 1886. 
Shell small, rounded-triangular, scarcely inflated, with high beaks which scarcely turn forward; 
lunule well defined but not impressed; ligament mostly immersed; surface covered with faint, concen- 
tric ridges and indistinct distal radial ribs, leaving the surface delicately decussated; cardinal teeth, 
three in each valve, rather feeble; left valve with an anterior lateral which fits into a socket in the right 
valve which is placed between two faint teeth. Color whitish or yellowish, usually marked with 
brown on the dorsal region, and often with irregular patches on the disk. 
Length, 11; height, 9.5; diameter, 4.6 mm. 
Culebra Island, one shell, at station 6087. 
Circe insularis, n. sp. Plate 55, fig. 2. 
Shell small, yellowish white, quite inequilateral, moderately convex, with a prominent, rather 
anterior, beak; sculpture of small, close-set, subequal, concentric undulations, with narrower interspaces 
and less pronounced on the umbones, crossed by fine radial strife, which are stronger toward the ends 
of the valves, where the interspaces sometimes become threadlike; lunule small, sharply defined, rather 
long and narrow; escutcheon absent; interior white, the margin in many specimens with aline sulcus, 
parallel to it around the shell; hinge normal; pallial line entire, but slightly truncate behind. 
Length, 5.5; height, 5; diameter, 3 mm. 
San Juan and Mayaguez harbors, Porto Rico; in the latter abundantly at station 6061, in 30 
fathoms, coral sand, but no living specimens were taken. 
Well distinguished from the other American species by its form and size. 
Superfamily CARDIACEA. 
Family CARI)lID4t. 
Genus CARDITJM Linnaeus, 1758. 
Shell ventricose, closed or gaping posteriorly; beaks prominent, subcentral; surface radiately 
ribbed; posterior slope sculptured differently from the front and sides; margins toothed; there are two 
interlocking cardinals and an anterior and posterior lateral in each valve; pallial line simple. 
Subgenus Trachycardium Morch, 1853. 
Cardium muricatum Linnaeus. 
Cardium muricatum Linnaeus, Syst. Nat., ed. x, p. 680, 175S; Reeve, Conch. Icon., ii, pi. vr, fig. 33, 1844. 
Shell subsolid, slightly oblique, scarcely gaping behind, having from thirty to forty ribs, each 
of which bears a row of solid, oblique scales; about eleven of the anterior ribs have these scales sloping 
