28 W. M. TATTEKSALL. 



narrower, rectangular in shape, outer margin unarmed, inner margin beset with a few 

 plumose setse. 



Antennal peduncle (Fig. l) equal in length to the antennular, but more slender; 

 last two joints subequal in length. 



Antennal scale (Fig. l) slightly longer than the last segment of the pleon and 

 twice as long as the antennular peduncle, about three and a half times as long as 

 broad, outer margin entire and terminating in a very strong spine, beyond which the 

 apex of the scale is but slightly produced ; spine on the basal joint short and acute. 



Mouth parts (Figs. 2, 3, 4, and 5) exhibit no salient points of difference from 

 those of the type species of the genus P. roseum, G. 0. Sars. 



JF'irst and second thoracic limbs (Figs. 6 and 7) agreeing in the main with those 

 figured by Sars for P. roseum, but a dactylus is distinctly visible among the dense 

 mass of plumose setse arming the terminal joints, though it is smaller and shorter 

 than the terminal joint ; exopods having the outer distal corner of the basal joint 

 round, though produced, and the flagelliform part composed of ten to twelve joints. 



Telson (Fig. 8) slightly shorter than the last segment of the pleon, tapering to 

 an evenly rounded apex which is one-third as wide as the base ; apex armed with a 

 median pair of plumose setse and four pairs of strong smooth spines, the innermost 

 and largest of which equals one-sixth of the telson in length ; distal half of the lateral 

 margins armed with five shorter spines. 



Inner uropods half as long again as the telson, armed with a single long spine 

 in the region of the inner posterior corner of the otocyst. 



Outer uropods about twice as long as the telson. 



Length of an immature female, 23 mm. By an error the specimen was described 

 in the preliminary report as adult. This is scarcely correct, since the incubatory 

 lamellae are still only about half developed, so that the adult female probably reaches 

 to nearly 30 mm. The specimen is badly mutilated, the third to the eighth thoracic 

 limbs being entirely absent. 



P. helgiccB is far and away the largest species of the genus yet described, none 

 of the other ten known species exceeding 15 mm., whereas adult specimens of this 

 species must reach to nearly 30 mm. It is most nearly related to P. sarsi Will.- 

 Suhni, described by Sars (1885) from the ' Challenger' collections for specimens taken 

 at Kerguelen Island. Besides the great difference in size (P. sarsi measures only 

 14 mm., adult specimens), the only other conspicuous difference is in the ocular 

 laminse. In P. sarsi the antero-lateral angles of the eye-plates are serrate, whereas 

 in P. belfficce they are quite smooth. Minor differences in the shape of the antennal 

 scale and telson may also be noted. The antennal scale in P. sarsi has the spine 

 terminating the outer margin less strong than in P. helgicce, while the apex of the 

 scale is more produced. The telson in P. sarsi has the apex more truncate than 

 P. helgicw and the lateral margins, according to Sars, bear eight short spines. 

 Mr. Holt, however, who has kindly examined the types of P. sarsi in the British 



