274 ISOPODA. 



whilst the third tribe, C. parasites, forms our restricted 

 family CYMOTHOID^E, the species of which are parasitic 

 on fishes, all their legs being alike in form and strongly 

 hooked for prehension, they are all, as well as the 

 antennae, short, and the latter are always inserted on 

 the underside of the head, beneath a prolongation of the 

 forehead, and the body is of a less firm consistence than 

 in the JEgidce, thus approaching the Bopyrida. The 

 species are numerous, but chiefly inhabitants of Tropical 

 Seas ; some few are, however, known to inhabit more 

 temperate climes, but no specimen has hitherto been 

 satisfactorily determined as having been found in our 

 own seas, although Cymothoa CEstrum* is introduced by 



* Cymothoa, Fabricius, is distinguished from the other genera of this tribe 

 or family by having all the segments of the pleon distinct and movable, the 

 pleon itself considerably narrower than the terminal portion of the pereion, 

 the last segment wider than long, and the legs tolerably strong and subche- 

 liferous. 



Cymothoa CEstrum 1 is distinguished from the other species of the genus 

 by having the anterior margin of the cephalon advanced and bent down 

 between the inner antennae, which are inserted widely apart, the first segment 

 of the body very large and advanced beyond the head on each side, and by 

 the lower edge of the bases of the fourth pair of legs armed with a strong 

 tooth. 



This species is found in the Atlantic Ocean and in the Seas of both Indies. 

 It attacks fish, and makes occasionally large wounds sufficient to cause the 

 death of the individuals attacked. 



1 Oniscus (Estrum, LINN. Syst. Nat. pp. 1059, no. 2, Faun. Suec. no. 



2053. Mus. Adolph. Frid. 89. FABRICIUS, 



Syst. Ent. p. 294. Sp. Ins. i. p. 375, no. 4. 



PALLAS, Spic. Zool., fasc. 9, p. 74, tab. 4, 



fig. 13, A. B. 

 Cymothoa (Estrum. LEACH, Edinburgh Enc. vii. pp. 405 and 433. 



Enc. Brit. Suppl. 1, p. 428. Trans. Linn. 



Soc. xi. p. 372. Diet. Sc. Nat. t. 12, p. 353. 



SAMOUELLE, Ent. Compend. p. 109. DES- 



MAREST, Cons. Crust. 309, pi. 47, figs. 6, 7. 



MILNE EEWAKDS, Hist. N. Crust. 3, 269. 



Regne An. (Crochard Edit.), Crust. pl.65,f.l. 

 Asellus <Estrum. OLIVIER, Enc. Meth. 4, 253. 



