MARINE ISOPODA OF NEW ENGLAND, ETC. 383 



following family. The remaining pairs of legs are fitted for walking. 

 The thoracic segments are siibeqiial in length and have the epimera well 

 separated, except in the first segment. 



The pleon may or may not be suddenly narrower than the last thoracic 

 segment, and, in our species, is composed of six distinct segments, of 

 which tlic last is large and scutiform. The uropods are composed of 

 a basal segment, oblique at the apex with the inner angle more or less 

 produced, and bearing two flattened, ciliated rami; they are distinctly 

 lateral, being inserted high uj) on the sides of the last segment. 



This family contains our largest Isopod, ^ga ]}mra., and to it should 

 j)robably be referred the huge Baihynomus gigantens A. Edwards, from 

 the Gulf of Mexico, measuring more than eleven inches in length. It 

 has usually been regarded as embracing the Cirolanidw. I have already 

 given my reasons for separating them, but have to regret my inability to 

 examine many types of genera apparently more or less intermediate in 

 position between ^ga and, on the one hand Cirolana, and on the other 

 Cymothoa and Livoneca. I have therefore retained the old classification 

 rather than to unite the following genera with the Gymothoidcc. 



Our two genera are most easily distinguished as follows : Eyes large 

 and approximate, ^ga,, p. 89 ; eyes wanting, Syscemis, p. 93. 



.Sjga Leach. 

 ^ga Leach, Trans. Linu. Soc, vol. xi, -p. 369, 1815. 



Eyes large ; palpus of maxillipeds five-jointed ; three anterior pairs of 

 legs terminated by strong curved claws ; posterior pairs slender, with 

 slender nearly straight dactyli ; pleon not suddenly narrower than the 

 thorax ; pleopods ciliated. 



This genus Is represented within our limits by a single species, which, 

 may be easily distinguished by its large approximate eyes. The basal 

 segments of the antennulfe are flattened and the flagellum is compara- 

 tively slender. The maxillipeds have a five-jointed palpus, which is 

 short and flattened and bent around the oral opening, and the inner 

 margins of the three terminal segments are pro^^ded with a row of 

 strong hooked spines, which are also found upon the outer maxillas, thus 

 forming two rows of short hooks on each side of the mouth, by means 

 of which the opening of the mouth can be closely applied to the fish on 

 which these animals prey. The inner maxillae are slender and styliform 

 and armed with sharp curved spines at the apex, and the mandibles are 

 also acute and fitted for piercing. The body is moderately convex, and 

 the last four pairs of legs are nearly alike ambulatory and of moderate 

 length, the last pair, when extended, scarcely surpassing the telson. 

 The pleon is composed of six distinct segments, and the basal segment 

 of the uropods is strongly produced at its inner angle, as usual in the 

 family. The pleopods are ciliated in the adults as well as in the young. 



