202 CRUSTACEA. 



the tail, or the middle one of its terminal fin, is transversely divided 

 by a suture. The 



Astacus communis ; Cancer nstacus, L. ; Roesel, Insect., Ill, 

 liv, vii. The Craw-Fish h<is its anterior forceps granulated, and 

 the inner edges finely dentatcd. There is a tooth on each side 

 of the snout, and two at its base ; the lateral edges of the seg- 

 ments of the tail form an acute angle. Its colour, which is 

 usually a greenish brown, is sometimes altered by accidental 

 circumstances. 



This species, which inhabits the fresh waters of Europe, lias 

 been more particularly studied, both as respects its anatomy 

 and habits, and the faculty enjoyed by the Crustacea of regene- 

 rating their antennae and feet Avhcn they arc either mutilated or 

 destroyed. When about to cast its shell, two stony concretions 

 are found in the stomach, formerly much used in medical prac- 

 tice as an absorbent, but now replaced by the carbonate of mag- 

 nesia. It conceals itself in hoks, or under stones, never quitting 

 its retreat except to search for food, Avhich consists of small 

 MoUusca and Fishes, and the larva? of Insects. It also feeds on 

 putrid flesh, the carcases of quadrui)eds, for instance, which 

 are placed as a bait for them in nets, or in the centre of fagots 

 of wood. They are also taken in their holes by the light of 

 torches. It changes its shell towards the end of spring. Two 

 months after coition, which takes place ventribus junctis, the 

 female produces her ova, Avliich are at first collected in masses, 

 and glued to the false feet, by means of a viscid hvunour. They 

 are of a reddish brown colour, and enlarge before they are 

 hatched. The young Astaci, at first extremely soft and precisely 

 like their parent, shelter themselves under- her tail, and remain 

 there several days, until their bodies acquire a certain degree of 

 solidity. 



The term of existence as.-;igned to tlie Astaci seems to be 

 twenty years and upwards, their size augmenting in proportion 

 to their age. Those are preferred for the table which inhabit 

 running streams of fresh water. A parasitic animal belonging 

 to the Annelilcs is found on their branchiae, long ago observed 

 by Roesel, but imperfectly known until the researches of M. 

 Odier *. 



The fresh- waters of North America produce another species, 

 the A. Bartonii, figured bv Bosc. — Hist. Nat. des Crust., II, 

 X, 1. 



A third inhabits the rice-fields of the same country, to which, 



according to Major Le Conte, one of the best naturalists of the 



United States, it is very injurious. 



In the fourth section, that of the Carides, the intermedial antennae 



are superior or arc inserted above the laterals : the peduncle of these 



latter is completely covered by a large scale. 



*■ See his Memoire siir le Branchiodellc, inserted in the M^m. de la Soc. d'Hist. 

 Nat. tome I, p. 69, et seq. 



