Australian Natural History. 1491 



Habits of two Crustacea of Port Jackson. — Two species of crabs 

 are very abundant in Farm Cove, Port Jackson, and I have met with 

 them elsewhere in Australia. Specimens of both, procured by me, 

 have been presented by the Earl of Derby to the British Museum, and 

 an account of their habits may prove of interest. 



Mycteris longicarpis, Latr. The sandy flats left by the tide are of- 

 ten partially covered with large bodies of this beautiful crab, the co- 

 lours of which (blue and white) I may mention cannot be preserved 

 in a dried specimen. On walking up to one of the large congrega- 

 tions of this species — for several thousands are often assembled to- 

 gether — the whole make off in one direction, betaking themselves, as 

 they proceed, to their holes in the moist sand. These latter are 

 merely temporary, for when hard pushed, the crabs form, by a kind of 

 circular or screwing motion, from right to left, a small perpendicular 

 hole, into which they sink to a depth of two or three inches. This 

 crab walks upon the tips of its claws, and, having long curved legs, 

 the semi-orbicular body is raised high above the ground. It moves 

 straight forwards, never sideways like many other Brachyuri, and is 

 by no means swift in its movements. A smaller species of the genus, 

 precisely similar in its habits, has received from Mr. McLeay the 

 MS. name of M. Latreillii. 



Gelasimus cordiformis, Latr. This curious little crab inhabits 

 muddy flats by the shore which are left dry at low water, also salt 

 marshes which are covered only at high tides, preferring the vicinity 

 of fresh or brackish water, especially running streams. It is found in 

 colonies, inhabiting holes in the mud, each of which harbours a male 

 and female, and to these they retreat with great swiftness upon being 

 disturbed. When pursued and overtaken, it erects its long first pair 

 of arms, and, with outstretched forceps, bites most vigorously. Spe- 

 cimens from Port Stephens are nearly double the size of the Port 

 Jackson ones. 



John McGillivray. 



