NO- 5-] ACCOU NT OF THE SPECIES. 27 



this form in honour of Dr. Nansen, who also took special notice of it 

 during the Expedition. 



Description. 



The largest specimens in the collection have a length of about 20 mm., 

 and this is accordingly a rather large-sized form, considerably exceeding in 

 size the type species, and about equalling in this respect the Caspian species, 

 P. platyceras (Grimm). 



The form of the body (see PI. IV, fig. 1), as compared with that of 

 P. littoralis, is rather more robust and less compressed, the back being 

 broadly rounded and perfectly smooth throughout. In the adult male, the 

 posterior division of the body, comprising the metasome and urosome, is fully 

 as long as the anterior ; but this is scarcely the case in the female, in which 

 the metasome is less powerfully developed. 



The cephalon is comparatively short, not nearly as long as the first 2 

 segments of the mesosome combined, and has the lateral lobes rather promi- 

 nent and distinctly angular at the tip (see also fig. 2). The lower edges are 

 deeply emarginated, to encompass the globular basal joint of the inferior 

 antennae, and behind the latter they project in an acute angle, the postantennal 

 corner. 



The segments of the mesosome gradually increase in size posteriorly, 

 none of them being, however, as large as the segments of the metasome. 

 The 4 anterior pairs of coxal plates are considerably deeper than the con'e- 

 sponding segments, and not very different in size. The 1st pair, however, 

 are a httle broader than the 2 succeeding ones, and slightly expanded 

 distally, with the tip transversely truncated (see also fig. 14). The 4th pairs, 

 as in the other species of this genus, are nan-ower than in most other 

 Lysicmassidce, and but very slightly emarginated behind. The 3 posterior 

 pairs of coxal plates are rather large, though somewhat less deep than the 

 anterior, and are rounded quadrangular in form, gradually diminishing some- 

 what in size posteriorly. 



The epimeral plates of the metasome are well developed, the 1st pair 

 being rounded, whereas the 2 posterior pairs are each drawn out behind to 

 an acute point. 



