406 M. A. Boeck on the Amjphipoda 



jointed ; the palpi of the first pair of maxillae are two-jointed, 

 and the inner lamellae are furnished with six ciliated hairs ; 

 the masticatory lamellae of the maxillipedes are large ; the palpi 

 are small and thin, and their fourth joint is a small claw. The 

 ovigerous lamellae are extremely large, furnished at the edges 

 with approximated long hairs ; the respiratory lamellae of the 

 last thoracic legs are of the same peculiar form that occurs in 

 Ichnopus ; the last two segments of the abdomen are coalesced, 

 and the telson is cleft ; the body is strongly compressed. 



Gammarus, Fab. — This genus, which, from including all 

 the Amphipoda, has gradually become reduced until it only 

 comprises those which have a compressed body with large epi- 

 mera, and long and slender antennae with a secondary nagellum, 

 has been very justly divided by Lilljeborg into two genera, — 

 1, Gammarus, in which the last abdominal foot is furnished 

 with lamellar branches, and, 2, Gammaropsis, in which these 

 are conical. The latter also differ from the former in their 

 smaller epimera and thick telson, and in having the inner 

 lamella of the first pair of maxillae small and furnished with 

 a single bristle, whilst in the others it is large and furnished 

 with numerous setae. We must also agree with Bruzelius 

 when he transfers these latter to the family Corophiidae. The 

 genus Gammarus thus formed includes three groups of Scan- 

 dinavian species. The first of these has the thorax fur- 

 nished with a keel, and the telson entire : this is H. Ratlike' s 

 genus Amathia, and includes the species Sabini, Leach, and 

 angulosus, H. R. The second group has the telson divided ; 

 the branches of the last pair of feet are furnished with spines 

 and ciliated hairs ; the hands are small : this includes the 

 typical species locusta, Linn., pulex, De Geer, and pwcilurus, 

 H. R. The last group has the telson divided, the last pair of 

 abdominal feet very long, the inner lamellae of the first pair 

 of maxillae smaller than in the preceding and furnished with 

 fewer ciliated hairs, and the second pair of hands generally 

 very large. This group includes the remaining known Scan- 

 dinavian species. 



Closely agreeing with the genus Gammarus is a species 

 which I found in the Christiania Fjord, which, however, dif- 

 fers therefrom in wanting the secondary flagellum on the 

 superior antennae ; but as there is a small tubercle in the place 

 usually occupied by the secondary flagellum, and the species 

 otherwise agrees essentially with the typical species, Gammarus 

 locusta, I do not think that it ought to be separated from the 

 genus Gammarus. 



G. Batei, mihi. — Of this species only one specimen, a male, 

 was found, at a little depth in the neighbourhood of Chris- 



