648 



THE VOYAGE OF H.M.S. CHALLENGER. 



is unequal on the two sides, both in length and proportion ; and the propodos of the three 

 posterior pairs of pereiopoda is more nearly equal in length to the carpos. 



This species still more closely resembles Pandalus longipes, A. Milne-Edwards, but 

 in the latter the first pair of antennae and the rostrum are longer. It also appears to be 

 nearly allied to Pandalus narwal (Fabricius), as described by Herbst, Latreille, Milne- 

 Edwards and Heller, which was taken in the Mediterranean. 



The Challenger species differs externally from either in having the serrature on the 

 dorsal crest more slender, closely packed, and extending posteriorly to the pyloric region. 

 Pandalus stylopus, Pandalus longipes and Pandalus narwal, all of which appear to me 

 to belong to this genus, have the teeth on the crest and base of the rostrum coarse, 

 whereas those on the distal portion of the rostrum are fine in Plesionika spinipes. 



Plesionika unidens, n. sp. (PI. CXJIL fig. 4). 



Eostrum twice the length of the carapace, crested and armed with teeth at the base ; 

 smooth on the upper surface to the apex, except for the presence of one tooth a little 

 posterior to the distal extremity ; the lower margin is furnished with six or seven teeth. 



First pair of antennas short, scarcely reaching beyond the extremity of the rostrum. 



Second pair having the flagellum but little longer. 



Pereiopoda slender but not remarkably long. 



Third somite of the pleon dorsally compressed to a straight carina posteriorly. 



Telson nearly as long as the outer rami of the rhipidura. 



Length, entire (male), 



of carapace, 



of rostrum, 



of pleon, 



of third somite of pleon, , 



of sixth somite of pleon, 



of telson, 

 Breadth of ophthalmus, . 



40 mm. (1*5 in.). 



11 



22 



29 



6 



6 



7 



35 



Habitat— Station 219, March 10, 1875; lat. 1° 54' 0" S., long. 146° 39' 40" E. 



north of New Guinea; depth, 150 fathoms; bottom, coral mud. 

 males and two (?) females. Trawled. 



Four specimens ; two 



This species has the rostrum very long and straight. It may readily be distinguished 

 from others by its having a solitary tooth on the upper margin of the rostrum, a little 

 posterior to the apex, the rest is smooth and straight until near the base, where there are 

 several teeth ; those just in front of the eye are the largest ; those behind the frontal 

 margin are the smallest and most closely compressed together, they are all laterally 

 compressed and stand like a crest above the eyes. From this crest a carina without 



