490 



pairs furnished with distinct calceolse. Anterior lip of the usual rounded 

 form ; posterior lip without any inner lobes. Mandibles strong and of 

 normal structure, palp rather robust, with the terminal joint falciform in 

 shape, and densely clothed with bristles. First pair of maxillae with the 

 basal lobe well developed and edged with numerous setae, palp having the 

 terminal joint scarcely expanded distally. Second pair of maxillse with the 

 lobes subequal in size. Maxillipeds with the masticatory lobes scarcely 

 larger than the basal ones, palp very robust, and having the terminal joint 

 densely setous. Gnathopoda rather strong, and quite alike in the two sexes, 

 carpus comparatively short, and forming inferiorly a rounded setiferous 

 expansion, propodos obpyriform in shape, with the palm very oblique and 

 imperfectly defined. Pereiopoda strongly developed, and edged with tufts of 

 small spines, the 3 posterior pairs moderately elongated, and having the 

 basal joint laminarly expanded. Branchial lamellae obliquely folded; incubatory 

 lamellae large and broad. Last pair of uropoda scarcely projecting beyond 

 the others, rami lanceolate in form, and edged with spines and setae. Telson 

 entire, with only a very slight emargination at the tip. 



BemarJcs. — The present genus was established by Rathke as early 

 as in the year 1837, to include a species from the Black Sea, A. carinata ; but, 

 as the generic name he proposed, Amatliia, was already appropriated, it was 

 changed in 1863 by Sp. Bate, to AmathiUa. The genus is chiefly distinguished 

 by the thick, dorsally-keeled body, the subequal and rather strongly built 

 antennae, the comparatively robust structure of the gnathopoda and pereiopoda, 

 and the form of the telson. Besides the above-mentioned exotic form, the 

 genus comprises 2 northern species, to be described below. The Gammarus 

 pinguis of Kroyer, which has generally been referred to this genus, ought in 

 my opinion to be removed as the type of a separate genus, as it difi^ers 

 considerably, in several points, from the true members of the present genus. 



5. Amathilla homari (Fabr.) 



(PI. 172, PI. 173, fig. 1.) 



Gammarus homari, C. Fabricius, Supplem. ent. Syst. p. 418. 



Syo. : Gammarus arenarius, O. Fabr. 

 » Gammarus Sabini, Leach. 

 » Amathia Sabini, Sp. Bate. 



Body in female very robust and rather tumid, in male considerably 

 more compressed. Mesosome and metasome distinctly cai-inated dorsally 

 throughout, the segments being elevated to compressed laminar pro- 



