ORDER DECAPODA — PINNOTHERES. 13 
it is supposed to be most closely allied. The shell of our species is more thin and membra- 
naceous ; the abdomen of the female is almost on a line with the front, has a greater trans- 
verse diameter, is reddish or yellowish, and the animal is larger. The P. pisum, on the con- 
rary, is of a more solid structure, orbicular, very convex, abdomen of the female much shorter, 
and is of a uniform dull brown or stone-color ; the terminal joints of the feet are long and 
incurved, whilst in the Oyster Crab they are short and nearly straight. 
This species, or at least the female, is usually found in the common oyster ; the male is 
more rare, and among thousands it is difficult to find one of that sex. They are eaten raw, 
and considered a great delicacy by epicures. 
(EXTRA-LIMITAL.) 
P. maculatum. (Sav, op. cit. Vol. 1, p. 450.) Body covered with very short deciduous dense hair; 
clypeus obtusely angulated, indented above the tip; two whitish spots. Color, black above, beneath 
yellowish ; female dull brownish immaculate. Male, 0°7; female, 0°4. Hab. Pinna muricata. 
Southern Coast. 
P. byssomia. (In. tb. p. 451.) Female. Thorax somewhat transversely oval ; clypeus hardly advanced, 
rounded, entire; hand not gibbous, near base of the thumb; tarsi unarmed. Male unarmed. Hab, 
(Byssomia) Saxicava distorta of the Southern coast. 
P. cylindricum. (In. Ib. p. 452.) Body transversely subcylindrical; anterior feet didactyle, equal ; 
second and third pairs nearly equal, and with punctured tarsi; fourth pair very robust, larger and 
longer than the anterior ones; posterior pairs very small. Eyes approximated, Male 0-3 long, 
0°65 brqad. Female 0°35 long, 0*75 broad. With the following, types of a new genus. Georgia. 
P. monodactylum, (Up. Ib. p. 454.) Thorax transversely subelliptical. Hands monodactyle; palm 
concave and ciliated in the middle; a spiniform angle instead of a finger, with a tooth at its base, 
and another at the base of the thumb, larger. Male, length 0+3, breadth 0°5. Hab. unknown, 
but presumed from the coast of America. 
Genus Ocyropa, Fabricius. Shield subquadrate or rhomboidal; the eyes very large, oblong oval, 
occupying at least half of the length of the peduncles, and commencing near the base. Feet 
adapted for walking. 
O. arenaria. (Say, op. cit. Vol. 1, p. 69. Epwarps, Vol. 2, p. 44, pl. 19, fig. 13. O. albicans, Bosc, 
pl. 4, fig. 1.) Shield very minutely granulated; the edges minutely serrate. Hands unequal, the 
largest serrate and dentate with spines: the third joint of the second and third pairs of feet without 
spines; tarsi of the second, third and fourth pair flattened, and enlarged at their extremities, Feet 
very hairy. Transverse diameter, 1+4. South-Carolina, Florida. 
