523 



Gen. 10. CheirOCratuS, Norman, 1865. 



Syn; Lilljeborgia, Sp. Bate (part). 

 Protomedeia, Sp. Bate (part). 



Body more or less slender, with the mesosome and metasome smooth, 

 urosome provided dorsally with dentiform projections and stiff bristles. Cephalon 

 without a rostrum, lateral corners forming a small rounded lobe, postantennal 

 ones projecting immediately beneath the former. Coxal plates comparatively 

 small ; 4th pair scarcely emarginated posteriorly. Eyes distinct, though rather 

 small. Superior antennas much shorter than the inferior, and provided with 

 a very small accessory appendage. Oral parts normal, except that the basal 

 lobe of the 1st pair of maxillae is very broad, and densely setiferous, and 

 that the palps of the maxillipeds are comparatively small and narrow. Gna- 

 thopoda in female rather feeble, and nearly equal, not subcheliform, the 

 propodos being very narrow, without any distinct palm ; the posterior ones 

 in male greatly developed, with the propodos exceedingly large, and of 

 different shape in the different species. Pereiopoda, as a rule, rather slender, 

 the 3 posterior pairs successively increasing in length, and having the basal 

 joint but little expanded. Last pair of uropoda rather elongated, rami 

 subequal, and narrow lanceolate in form, edged with slender spines. Telson 

 small, and divided by a deep incision into 2 lobes, each of which is 

 spinous at the tip. 



Remarks. - - This genus was established in the year 1865 by Norman, 

 to include a supposed new form, which he named C. mantis. Boeck, however, 

 pointed out that this form is identical with the Gammarus assimilis of 

 Lilljeborg, and that the Gammarus Sundeivalli of Rathke ought to be included 

 in the same genus. From the other known genera of Gammaridse, this is at 

 once distinguished by the different mutual longitudinal relation of the 2 

 pairs of antennae, and by the structure of the gnathopoda. In other respects, 

 however, it shows itself to be a true Gammarid. The species of this genus 

 are very nearly related, and it is indeed a matter of great difficulty to 

 distinguish the females of the different species from each other, whereas the adult 

 males are at once recognizable by the rather different shape of the posterior 

 gnathopoda. According to Boeck, the Gammarus pugetensis of Dana ought to 

 be referred to this genus. Besides that species, the genus comprises 4 

 northern species, all of which belong to the fauna, of Norway, and will be 

 described below. Two of these species are now for the first time 

 established. 



