282 MARINE INVERTEBRATES 



tions, making two spine-like projections which bend forward. The 

 four posterior pairs of legs are more or less hairy ; the chelae 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. oreijonensis in being purple in 

 color, with mottled claws, and in haying 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 described above, but is considerably larger, 

 and the carapace is banded with color. 



FAMILY OCYPODIDJE 



GENUS Ocypoda 



O. arenaria, the sand- or ghost-crab. The name Ocypoda means 

 " swift-footed," and, as it implies, 'his species is especially noted for its 

 rapidity of movement. These crabs are the opposite of the strong-armed, 

 thick-shelled, slow-moving Cancroidu;. 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 over the sand. They are also dexterous in 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 corner's 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 chelae 

 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 hcdrs. (Plate LXIII.) 



GENUS Uca 



IT. minax(Gelasimu8 minax), U. pugnax (Gelasimuspugnax), 

 U. piigilatar (Gelasimu&pugUator), the fiddler-crabs. These species 



