282 MARINE INVERTEBRATES 
tions, making two spine-like projections which bend forward. The 
four posterior pairs of legs are more or less hairy; the chele are rather 
large in proportion. The male is about one inch across and the female 
is one third less in size. The general color is yellow. .H. nudus is found 
in the same localities, and differs from H. oregonensis in being purple in 
color, with mottled claws, and in having the denticulations less pro- 
nounced and the walking-feet devoid of hairs. It is also a little 
larger. (Plate LXIII.) 
Genus Pacygrapsus 
P. crassipes. A species very common on the California coast south 
of San Francisco. This crab is similar in general features to the 
purple and yellow ones deseribed above, but is considerably larger, 
and the carapace is banded with color. 
FAMILY OCYPODIDE 
Genus Ocypoda 
O. arenaria, the sand- or ghost-crab. The name Ocypoda means 
“ swift-footed,” and, as it implies, this species is especially noted for its 
rapidity of movement. These crabs are the opposite of the strong-armed, 
thick-shelled, slow-moving Cancroide. An instance is told of a collector 
having great difficulty to keep up at full run with one which he chased for a 
considerable distance overthesand. Theyarealsodexterousin burrowing, 
and live in holes, often three feet deep, dug perpendicularly into the 
sand. They wander far from their burrows when the tide is out, and 
every little while raise their stalked eyes and stand on tiptoe to look 
about. If alarmed, they run with great rapidity to the nearest burrow, 
or, if danger is close, press themselves on the sand until an attempt is 
made to touch them, when they again dart away rapidly, and in running 
hold their bodies high, and double and dodge so that it is difficult to 
catch them. Ocypoda is colored almost exactly like the sand, and this 
mimicry, together with its fleetness, makes it interesting to note and 
difficult to capture. It inhabits sandy beaches above tide-mark from 
Long Island to Brazil, and subsists largely upon the beach-fleas, which 
inhabit the same localities. It springs upon them, very much as a cat 
catches a mouse. The carapace of this species is almost square in outline, 
and on the anterior corners ends in a spine. A small portion of the 
carapace folds down like a band between the eyes. On each side of this 
band, and extending across the front, are large grooves for the eye- 
stalks. The body is about an inch thick; the first joints of the chele 
are toothed; one chela is a little longer than the other, and both are 
coarsely granulated. The other four pairs of legs are thickly fringed 
with hairs. (Plate LXIII.) 
Genus Uca 
U. minax (Gelasimus minax), U.pugnax (Gelasimus pugnax), 
U. pugilator (Gelasimus pugilator), the fiddler-crabs. These species 
