268 THE VOYAGE OF H.M.S. CHALLENGER. 



of the type, but differs from that of Penseus serratus, with which they were found 

 associated. In these specimens the telson is armed with two teeth posterior to the two 

 lateral spines, and therefore Penseus rectacutus may be only a variety. 



Penseus serratus, Spence Bate (PI. XXXVII. fig. 1). 



Penseus serratus, Sp. B., Ann. and Mag. Nat. Hist., ser. 5, vol. viii. p. 182, 1881. 



Eostrum slightly arched, armed with a series of small teeth, twelve or thirteen in 

 number, between the base and the apex, and one distant on the gastric region ; lower 

 margin fringed with long, ciliated hairs, each of which stands on its own defined 

 point of attachment. Posterior somite of the pleon more than twice the length of the 

 penultimate. Telson nearly as long as the inner branch of the rhipidura, terminating in 

 a styliform point, and armed on each side with a long and rigid tooth, and at some 

 little distance anteriorly with two minute separate spines, the intervening space being 

 fringed with hairs. 



The ophthalmus is large, and the peduncle of the first pair of antennae is rather 

 longer than the rostrum. The flagella, in a" young specimen, are about as long as their 

 peduncle ; they are damaged in the others. The prosartema is pointed, the stylocerite 

 short, and the scaphocerite of the second pair reaches to the extremity of the rostrum. 



Length of the largest female, 114 mm. (4"5 in.) ; of the largest male, 76 mm. (3 in.). 



Habitat— Station 173, July 24, 1874; lat. 19° 9' 35" S., long. 179° 41' 50" E. ; 

 off Matuku, Fiji Islands; depth, 315 fathoms; bottom, coral mud. 



Station 184, August 29, 1874; lat. 12° 8' S., long. 145° 10'E.; Torres Strait; depth, 1400 

 fathoms; bottom, Globigerina ooze; bottom temperature, 36 O- 0. One specimen, young. 



Length, 26 min. (1 in.). 



The surface of the animal is smooth and even polished. It is slender in general 

 shape — a circumstance that is probably partly due to the length of the sixth or posterior 

 somite of the pleon, which is rather more than twice the length of the fifth. The rostrum, 

 instead of being horizontal, rises slightly from the base and is depressed at the apex, so 

 as to give it a slightly arched appearance. The low T er margin is without teeth, but fringed 

 with hairs, each of which is extremely long and ciliated, stands upon its own little elevated 

 point of attachment, and is generally of a dark colour. The upper or dorsal surface is 

 serrate with small teeth, placed closely together towards the base, but distantly separated 

 towards the apex ; on the gastric region a solitary tooth stands apart from the rest, at 

 the extremity of a carina, which disappears until the fourth somite of the pleon, where 

 it reappears in the form of a small ridge. This ridge becomes larger on the fifth and 

 sixth somites, having its posterior extremity cleft on the fourth and fifth, and produced to 

 a small tooth on the sixth. The telson is not so lona; as the inner branch of the 

 rhipidura, and terminates in sharp and styliform points (fig. lz), it is broadly channelled 



