26 G. 0. SARS. CRUSTACEA. [norw. pol. Exp. 



which are quite distinct from the previously known arctic form, P. littoralis, 

 but, on the other hand, are so closely related to the 2 Caspian species, that I 

 am much inclined to regard them as the primitive forms from which the 

 latter are descended. 



6. Pseiidalibrotus Ncmseni, n. sp. 

 (PI. IV, V). 



Specific Characters. Body comparatively robust, with broadly rounded 

 back. Cephalon with the lateral lobes rather prominent and angular at the 

 tip; postantennal angle well marked. Eyes of moderate size, oval, somewhat 

 contracted above. 1st pair of coxal plates but slightly expanded, and obtusely 

 truncated at the tip. The 2 posterior pairs of epimeral plates of metasome 

 acutely produced behind. 1st segment of urosome with a distinct saddle-hke 

 depression dorsally. Antennae rather slender and elongated, especially in the 

 male, flagellum of both pairs in the latter provided with well developed cal- 

 ceolae, accessory appendage of the superior ones 4 — 5 articulate. Anterior 

 gnathopoda somewhat smaller than in the type species; posterior ones with 

 the propodal joint transversally truncated at the tip, carrying the small dac- 

 tylus about in the middle of the terminal edge. The 3 posterior pairs of 

 pereiopoda much less slender than in the type species, with the basal joint 

 very large and lamellar, oblong oval in form, and coarsely serrate behind; 

 last pair considerably shorter than the preceding pair, with the outer part 

 scarcely more than half the length of the basal joint. Last pair of uropoda 

 comparatively short, scarcely reaching beyond the others, structure about as 

 in P. littoralis. Telson rather large, reaching to the end of the basal part 

 of the last pair of uropoda, rounded quadrangular in form, tip slightly 

 insinuated. Length of adult male about 20 mm. 



Remarks. This species is easily distinguishable from P. littoralis by its 

 more robust form, and more especially by the structure of the posterior pairs 

 of pereiopoda, the outer part of which is remarkably short in proportion to 

 the basal joint. It more resembles the Caspian species, P. platyceras (Grimm), 

 to which, indeed, I believe it stands in direct genealogical relation, although, 

 on a closer comparison, several differences may be found between them, 

 which make it necessary to keep the two species apart. I propose to name 



