424 



catapJiractus, wliicli evidently belongs to the genns here treated of, though he 

 also included in it some of the species of Costa. In 1870 Boeck restricted 

 the genus to the limits now generally adopted, and substituted the generic 

 name Trifropis instead of Amphithonotus, which was already' appropriated to 

 a genus of Reptilia. As, howover, the name proposed by Boeck was also 

 appropriated, Prof. Sidney Smith changed it in 1883 to RharJiotropis. The 

 genus is evidently nearly allied to Eusirus, in spite of the rather different 

 shape of the gnathopoda, and ought therefore undoubtedly to be included in 

 the same family. It comprises, like the genus Eusrnis, 5 Norwegian species. 

 2 of which are now for the first time established. Besides these, 4 other species 

 have been described, viz., the North American form i?. cataphractus Stimpson, 

 a form, li. liergueleni Stebbing, from the Challenger Expedition, a Greenlandic 

 species, II. oculata Hansen, and a form recently described by Mr. Chevreux 

 from the Expedition of the «Hirondelle» as Tritropis grimaldii. 



n. Rhachotropis aculeata, (.Lepechin). 



(PI. 149). 



OniscHu aculeatm, Lepechin, Acta Tetropol. 1778. 1., p. 2'J7, PI. 8, ii^'. I. 



Sj-n. : Talitrus Edwardsii, Sabine. 



> Amphitlioo Edwardsii, Owen. 



» Ampliitlionotus Edwardsii, Sp. Bate. 

 » — aculeatus. Goes. 



Body rather thick, with the antei-ior part of the back bi'oadly vaulted. 

 The last 2 segments of raesosome and those of metasome distinctly tricarinate, 

 dorsal keel elevated to strong, posteriorly-pointing spines, having on the 

 metasome in front a small secondary projection, subdorsal keels likewise 

 produced in each of the segments to spiniform processes. First segment of 

 urosome with 2 successive dorsal projections. Cephalon rather thick in its 

 posterior part, and somewhat gibbous above, rostral projection very large and 

 horizontally projected, reaching nearly to tlie tip of the basal joint of the 

 superior antennse, lateral corners forming a narrow triangular, and somewhat 

 deflexed lobe, defined posteriorly by an angular incision. First pair of coxal 

 plates somewhat securiform in shape, both the anterior and posterior corners 

 being produced to a sharp deflexed point, distal edge between both slightly 

 concaved; the 2 succeeding pairs terminating each in a short, recurved point; 

 4th pair scarcely larger than the 2 preceding pairs, and truncated at the tip; 

 5th and Gth pairs with a slight ridge running across the posterior lobe. Last 

 pair of epimeral plates of metasome obtusely rounded at the lateral corners, 



