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



The first pair of pleopoda in the female has the inner branch reduced to a rudimentary 

 condition. There was no male taken at Station 204. 



The sixth pair, which forms the movable plates of the rhipidura, has the inner plate 

 a little, and the outer plate much longer than the telson ; the outer is obliquely and 

 longitudinally traversed by a groove which continues to just within the outer extremity 

 of the diaeresis, on each side of which groove is a longitudinal ridge that, becoming- 

 confluent beyond it, traverses the outer margin of the plate and terminates in a well- 

 developed but not large tooth that falls considerably short of the distal extremity, which 

 is thickly fringed with ciliated hairs. The diaeresis is rigid and situated near the middle 

 of the plate. The inner branch is longitudinally traversed in the median line by a 

 straight groove, its margins being elevated to a ridge, the inner of which, not shown 

 in the figure, bifurcates not far from the base and abruptly turns away and joins the 



Pcnseus rectacutus, n. sp. (PI. XXXVI. fig. 2). 



Rostrum horizontal, straight, pointed, armed on the upper surface with twelve teeth 

 which diminish in size anteriorly to a rudimentary condition, and one solitary distinct 

 tooth standing over the gastric region. The lower margin of the rostrum is straight 

 and slightly elevated anteriorly, the outer orbital tooth is prominent but not large, 

 and so is the one on the hepatic region. The dorsal surface of the carapace behind 

 the gastric region exhibits a tendency to become carinated, which disappears entirely 

 on the pleon until the posterior division of the third somite is reached, where it 

 increases to a distal carina which culminates in a sharp tooth at the posterior extremity 

 of the sixth somite. 



The eyes are large, and the first pah - of antennae has the peduncle of about the same 

 length as the rostrum, and the flagella are equal to one another in length. 



The telson in the typical specimen has two small articulating spines on each side, 

 beyond which it has been broken off. 



Length (female), 114 mm. (4"5 in.). 



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

 Matuku, Fiji Islands; depth, 315 fathoms; coral mud. Five females. Dredged. 



Station 209, January 22, 1875; lat. 10° 14' N., long. 123° 54' E. ; between Bohol and 

 Zebu; depth, 95 fathoms; bottom, blue mud; bottom temperature, 7l°'0. One female. 

 Trawl and dredge both used. 



This species comes near to Penseus monoceros, Fabricius, as described by Milne- 

 Edwards, but differs in having the rostrum a little longer and the denticles on the upper 

 margin rather more numerous, in having the flagella of the first pair of antennae longer, 

 and in the sides of the telson being armed with two or more spines. 



