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



Length, entire, 



,, of carapace, 



,, of rostrum, 



„ of pleon, 



„ of third somite of pleon, 



,, of sixth somite of pleon, 



„ of telson, 



Habitat.— Station 304, December 31, 1875 ; lat. 46° 53' 15" S., long. 75° 12' 0" W.; 

 Port Otway, Messier Channel; depth, 45 fathoms ; bottom, green sand. Eight specimens; 

 all but one being more or less damaged. Dredged. 



This species forms an interesting transition to Plesionika. The posterior spines 

 on the frontal crest of the dorsal surface, when examined under the microscope, 

 are seen to have a distinct articulation with the base, but their form corresponds with 

 that of the succeeding teeth on the rostrum instead of being cylindrical and spine-like as 

 seen in other species. Each of these spines is anteriorly serrate with three little 

 teeth that have the points rounded or directed towards the base, and this serrature is 

 continued on the teeth on the rostrum, but decreases in importance anteriorly on each 

 succeeding tooth, so that it is scarcely visible on the most anterior, which stands near the 

 centre of the rostrum. Beyond the most anterior tooth the margin is smooth and 

 curved slightly upwards, terminating in an apex with two small teeth, of which the upper 

 is the smaller and the lower the most advanced. The inferior margin is convex in a 

 curve that is a little more arched than that of the upper margin, and furnished with four 

 small teeth that lie almost parallel with it, and are scarcely distinguishable by an ordinary 

 lens. The frontal margin of the carapace is furnished with a strong antennal tooth and a 

 small one at the fronto-lateral angle. 



The body of the animal is generally smooth and exhibits no differential specific 



feature. As in most of the species in this and other allied genera the third somite is 



arcuate, a condition that produces a gibbous appearance when the animal is extended. 



The ophthalmopoda are pear-shaped and furnished with a distinct and almost isolated 

 ocellus. 



The first pair of antennas has the peduncle about half the length of the rostrum, 

 having the first joint deeply excavated to receive the ophthalmopod, and furnished with 

 a sharp-pointed stylocerite. The flagella reach a little beyond the extremity of the 

 rostrum, the. outer being the stouter and furnished with hairs and numerous long 

 membranous cilia that appear to increase in number towards the distal extremity ; the 

 inner is much more slender than the outer, a little longer, and supports only a few hairs. 



The second pair of antennas carries a scaphocerite that is armed with a strong tooth 

 near the rounded distal extremity, and a flagellum which, although broken at the 

 extremity, yet shows evidence of being nearly as long as the animal. 



