A 
REVISION OF THE ASTACIDA. 
Tue family Astacid, in a strict sense, is equivalent to the genus Asta- 
cus, as limited by Milne Edwards in 1837.* Thus restricted, it includes only 
fresh-water species, the crayfishes proper, — animals closely related to the 
marine family of lobsters, or Homaridxe (Homarus, Nephrops, Nephropsis, 
Enoplometopus, Phoberus), from which they are distinguished by having 
the last segment of the thorax movably articulated with the preceding 
segment, and by having the podobranchix (or gills borne on the thoracic 
limbs) closely united to the epipodites (or external branches of the limbs), 
to the more or less complete suppression of the lamellar portion of the 
epipodite. On the other hand, the Astacide lead, through such forms as 
Thaumastochelest and Calocaris, to the fossorial Thalassinide. 
Thus limited, the Astacidze are Macrourous Decapod Crustacea, with 
carapace produced into a rostrum in front, and divided by a transverse 
groove (cervical groove); narrow thoracic sterna; posterior thoracic somite 
united to the preceding somite by a movable joint; second to sixth abdomi- 
nal somites with a broad descending lateral plate (pleuron) on each side, 
which protects the abdominal appendages; antennules terminated by two 
filaments; antennz furnished with a movable external scale or squame ; + 
first pair of legs much enlarged, chelate ; second and third pairs of legs with 
small chelx; last two pairs of legs not chelate; first pair of abdominal 
* Histoire Naturelle des Crustacés, Tom. II. p. 329. 
+ A genus founded by Wood-Mason (Proc. Asiatic Soc. Bengal, 1874, p. 181) for the reception of 
Astacus zaleucus Willemoes-Suhm, brought up by the “Challenger” from a depth of 450 fathoms, near 
Sombrero Island, West Indies. See Trans. Linn. Soc. London, 2d Series, Vol. I., Zoél., pp. 48-50, 
Pl. X. fig. 1. Until the structure of the gills is known, it is impossible to say whether, from the sum of its 
characters, Thaumastocheles should be placed among the Astacide or among the Thalassinide. 
$ The antennal scale is very small in Asfacoides Madagascariensis Aud. et M. Edw. 
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