471 



Gen. 2. Atylus, Leach, 1S17. 



Body, in general appearance, resembling that of the preceding 

 genus, being highly compressed and distinctly keeled dorsally, with some of 

 the segments elevated to posteriorly pointing projections. Urosome with a 

 single dorsal process at the end of its 1st segment. Cephalon more or less 

 produced in front, and having the postantennal corners distinct and defined 

 from the lateral ones b}- an angular incision. Coxal plates comparatively 

 small. Antennae not very slender, and subequal in length, the superior ones 

 with a small nodiform accessory appendage. Mandibles with the palp very 

 fully developed. Second pair of maxillge with the outer lobe much longer 

 than the inner. Maxillipeds comparatively large, masticatory lobes of moderate 

 size, palp rather strong. G-nathopoda comparatively^ short, but rather strongly 

 built, having the propodos much dilated. Pereiopoda comparatively short; 

 last pair with the basal joint very much expanded, and having the dact3'lus 

 recurved. Branchial lamellae simple. Last pair of uropoda reaching scarcely 

 beyond the others, rami subequal and edged with slender bristles. Telson of 

 moderate size, more or less deepl}'^ cleft, terminal lobes obtusely pointed. 



Eemarls. — The present genus, established by Leach as early as in 

 the j-ear 1S17, is nearly allied to the preceding one, though differing rather 

 markedly in a few points. Thus the superior antennae are clearly distinguished 

 by tlie presence of a distinct, though small accessory appendage, and both 

 pairs are. moreover, far less slender than in that genus, and subequal in 

 length, further, the mandibular palps are very large, and the palps of 

 the maxillipeds much more fully developed than in Parati/Jiis; finally, the 

 gnathopoda are comparatively more strongly built, and the telson of a sonie- 

 wliat different shaj)e. Besides the arctic species described in the sequel, the 

 antarctic form, AtyJits huxleyanus, moat probably belongs to this genus. 



6. Atylus carinatus (Fabr.). 



(PI. 166, fig. 1). 



Gammarus carinalus, Fabricius, Entom. Syst. II. 616. 



Syn. : Amphitlioe carinata, Kroyer. 

 » Parampliithoe carinata, Goes. 



Body rather elongated and highly compressed, with the back distinctly 

 keeled throughout, the carina being in tlie last 3 segments of mesosome and 



