TANAIS. 119 



ISOPODA. TANAIDJS. 



VAOANTIA. 



Genus TANAIS. (Andouin and Milne Edwards.*) 



Zeuxo. TEMPLETON, Trans. Ent. Soc. ii. (1836). 



Crossurus. RATHKE, Nov. Acta. xx. 



Anisocheirus. WESTWOOD, Ann. Sc. Nat. xxvii. (1832). 



Generic character. Body elongated. Cephalon and first seg- 

 ment of pereion confluent. Antennas short, subequal. First 

 pair of gnathopoda very large, didactyle ; second pair slender, 

 simple, and assimilating to the pereiopoda. Pleon five-jointed, 

 fourth joint short, fifth terminated by a pair of single-branched 

 filamentary uropoda. 



IN the large size of the first pair of didactyle legs, 

 and in the confluence of the head and first segments 

 of the body, this genus agrees with Apseudes, but the 

 second pair of legs are slender and simple, and the 

 tail is terminated by two short slender appendages com- 

 posed of but very few articuli. The antennas are also 

 short, being nearly equal in length, although the inner 

 or superior pair are much stronger than the outer pair. 



The body is small and has the sides nearly parallel. 

 The head and first segment of the body are so closely 

 soldered together that little or no trace of their separa- 

 tion is visible from above; the anterior portion of the 

 head is produced into a point. The eyes are porrected 

 on short footstalks, which are movable in the males, 

 according to Fritz Miiller, but which, according to Van 

 Beneden, are completely immovable. The upper or 

 inner antennae are seldom so long as the head and fol- 

 lowing segment; they are straight, directed forwards and 

 downwards, and are much thicker than the lower pair ; 

 they are formed of a peduncle which consists of three 



* Resume (not Precis) d. Ent. p. 182 (without description 1829), pi. 

 xxix. fig. 3, " Tanais de Costa," not "Tan. Cavolini." (The reference by 

 M. Edwards to Ann. Sci. Nat. xiii. 288, is erroneous, being intended for 

 Rhoea.) Latr. Cours d'Ent. 403. 



