A 



REVISION OF THE ASTACID^E. 



THE family Astacidrc, 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 Homaridae (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 podobranchiae (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 Astacidae lead, through such forms as 

 Thaumastochelesf and Calocaris, to the fossorial Thalassinidse. 



Thus limited, the Astaciclte 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; antennae furnished with a movable external scale or squamejt 

 first pair of legs much enlarged, chelate ; second and third pairs of legs with 

 small chela? ; last two pairs of legs not chelate ; first pair of abdominal 



* Histoire Natuvelle ties Crustaccs, Tom. II. p. 329. 



f A genus founded by Wood-Mason (Proe. Asiatic Soc. Bengal, 1874, p. 1ST) for the reception of 

 Astacus zuleurus Willcmoes-Snlini, brought up by the "Challenger" from a depth of 450 fathoms, near 

 Sombrero Island, West Indies. See Trans. Linn. Soc. London, 3d Series, Vol. I., Zool., pp. 4S-30, 

 PI. 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 Astacidrc or among tlie Thalassinid<e. 



% The antennal scale is very small in Astacoides Madayaseunensis Aud. et M. Edw. 



1 



