MOLLUSC A OF PORTO RICO. 
463 
Melina semiaurita Linnteus. 
Ostrea semiaurita Linnaeus, Mus. Lud. Ulric., p. 535, 1764. 
Perna bicolor C. B. Adams, Proc. Bost. Soc. Nat. Hist., v, 1845, p. 9. 
Concha semiaurita Chemnitz, Conch. Cab., vn,p. 250, pi. 59, fig. 580, 1784 (nonbinomial). 
Shell small, subquadrate, solid, somewhat inflated, very irregular, hinge line having three or 
four large pits in each valve; byssal notch small. The surface is covered with strong, irregular, scaly 
ridges; the base in adult shells often projects somewhat tongue-like, and to some distance below the 
nacreous layer. Color ashy to blackish. 
Length, 12; height, 16; diameter, 8 mm. 
San Juan, two specimens. 
This species grows in the crevices of corals and rocks and is as variable in form as any oyster. It 
may prove to be only a littoral form of the preceding species. It is the Perna chemnitziana of 
d’Orbigny, 1846. 
Family PTERIID45. 
Genus PTERIA Scopoli, 1777. 
Shell suborbicular or oblique, thin or solid, slightly inequivalve, the left valve being more convex 
than the right; right valve with a distinct byssal notch and sinus near its upper anterior part; valves 
winged before and behind; hinge with rudimentary pseudocardinals and laterals; ligament elastic, 
placed in an oblique fossette; inner shell layer brilliantly nacreous, not extending to the shell border. 
Pteria radiata Leach. 
Avicula radiata Leach, Zool. Miscellany, I, p. 98, pi. xliii, 1814. 
Shell suborbicular or subquadrate, rather thin, somewhat inflated, more or less oblique, the 
hinge about as long as the body of the shell, moderately winged before and behind; surface, especially 
toward the edges of the shell, having radiating rows of strong, somewhat elongated scales, more or 
less variegated with purple, brown, and whitish, sometimes feebly rayed; pseudocardinals faint, single 
in each valve; laterals single in the left valve and double in the right; nacre brilliant, surrounded by 
a wide, prismatic border. 
Length, 40; height, 38; diameter, 16 mm. Length of another, 50; height, 50; diameter, 18 mm. 
Off Boca Prieta; Mayaguez Harbor, Porto Rico. 
Sometimes the surface is almost smooth. 
Superfamily OSTRACEA. 
Family OSTREIDiE. 
Genus OSTREA Linnaeus, 1758, 
Shell irregular, fixed by the left or lower valve which is excavated; right valve generally plane 
or concave, always less convex than the left, often plaited or foliaceous,-and having a prominent 
beak; ligamental area triangular or elongated; structure subnacreous; hinge edentulous; adductor 
impression single. 
Ostrea virginica Gmelin. 
Ostrea virginica Gmelin, Syst. Nat., p. 3336, 1792. 
Ostrea rostrata Sowerby, Conch. Icon. , xvni, pi. vi, 1871. 
Shell elongated, irregular, elliptical oval, or nearly circular, straight or curved; left valve usually 
excavated; right valve generally flat, sometimes concave or a little convex; lower valve with a strong, 
usually elongated beak, its hinge having a wide channel in center and. marked with lines exhibiting 
the successive removes of the cartilage; upper valve with a shorter beak, with a faint ridge in the hinge 
area opposite channel of left valve; muscular impression near center strong and large, often dark. 
Mayaguez; Puerto Real, Porto Rico; Ensenada Honda, Culebra. 
It is almost impossible to give a description that will cover all the forms of this protean species, 
which varies infinitely with the locality and environment in which it grows. Specimens in northern 
waters attain a length of a foot, and where they are crowded in the beds are long and tongue-like. 
Those living on flat stones and timber are often nearly circular. The Porto Rican specimens for the 
most part are attached to the swinging aerial roots of the mangroves. 
