39 



Remarks. — This peculiar form may at once be distinguished from our 

 other Tanaids, at least in the female sex, by the rudimentary condition of the 

 metasome. In both sexes, moreover the structure of the chelfpeds and uropoda 

 may serve for recognizing the species. 



Occurrence. — I have met with this form occasionally together with other 

 Tanaids in several places, both on the south and west coasts of Norway, as far 

 north as Kvalo, in depths ranging from 50 to 150 fathoms. 



Gen. PseudOtanaiS, G. O. Sars, 1880. 



Generic Characters. — Body short and stout, not very different in the 2 sexes, 

 with the cephalosome more or less contracted in front, and having no distinct 

 ocular lobes. The 3 anterior segments of mesosome much shorter than the 2 

 succeeding ones. Metasome not broader than the mesosome, and composed of 6 

 well-defined segments. Eyes imperfectly developed, or altogether wanting. Superior 

 antennae of same structure in the 2 sexes, very narrow, 3-articulate ; inferior an- 

 tennae almost of same size as the superior. Mandibles comparatively small, cut- 

 ting part in the right mandible simple, minutely serrulate, in the left one 

 provided with a rather large secondary lamella, molar expansion in both mandi- 

 bles very narrow, styliform. Maxillipeds with the masticatory lobes coalesced. 

 Chelipeds large, of a similar structure in the 2 sexes, hand very much elongated, 

 fingers narrow and acuminate. Pereiopoda slender and elongated ; ] st pair somewhat 

 differing from the others, which are subsimilar in structure, each having a remark- 

 ably strong, cultriform spine at the end of the carpal joint inside. Pleopoda 

 sometimes wanting in female. Uropoda biramose, both rami well-defined and bi- 

 articulate. Incubatory pouch formed by only 2 lamellae, issuing from the bases 

 of the 4th pair of pereiopoda. 



Remarks. — This genus agrees with the genus Tanais in the less conspicu- 

 ous sexual difference, and in the structure of the incubatory pouch, but otherwise 

 differs very materially, both as to its outward appearance, and to the structure 

 of the several appendages. It comprises as yet 7 species, 3 of which belong to 

 the Norwegian fauna, and will be described below. Of the other 4, the one, 

 P. Willemoesi (Studer), has been taken off the Kerguelen Islands, the second, P. 

 mediterranea G. 0. Sars,. at Spezia, and the other 2, P. af finis and P. crassi- 

 cornis Hansen, in the Kara Sea. 



