Mr. C. Spence Bate on Diastylis borealis. 85 



Diastylis borealis. PI. I. fig. 3. 



The carapace is much deeper anteriorly than it is posteriorly; 

 the antero-lateral processes of the mandibular segment do not 

 meet on the dorsum, but form two distinct arcuate margins. 

 The infero-anterior margin is strongly serrated. The rostrum 

 is short and blunt at the extremity. The anterior surface of the 

 carapace is ornamented with several short spines, placed in rows, 

 that traverse a direction coinciding somewhat with that of the 

 anterior margin. The posterior portion of the surface possesses 

 a reticulated appearance, owing apparently to the cellular struc- 

 ture of the tissue. The margins of the exposed segments of the 

 pereion are smooth, and the last is produced posteriorly into a 

 strong tooth. 



The antennae are short ; the superior do not extend beyond 

 the extremity of the rostrum, the peduncle being shorter and 

 broader than the flagellum. It carries four cilia — two on the 

 terminal articulus and one on each of the others. The inferior 

 antennae are longer than the upper, and consist of a peduncle, 

 of which only two joints are exposed. The flagellum consists of 

 six articuli, of which the first is the shortest, the second is the 

 longest, and the remaining four gradually decrease in length 

 towards the extremity; a small secondary appendage, consist- 

 ing of two or three articuli, is attached to the extremity of the 

 peduncle. 



The appendages attached to the first and second somites of 

 the pleon of the male are bifurcate at the extremity. The third 

 and fourth somites have two pairs of strong hairs corresponding 

 in position to the appendages in the two previous somites; the 

 fifth somite is without appendages or hairs, and is half as long 

 again as the preceding. The sixth somite is about the same 

 in length as the fifth, and terminates laterally in two long ap- 

 pendages (pleopoda), the basal joint of which is rather more 

 than twice the length of the sixth somite, and is furnished with 

 spines on the inner side : at the extremity of the basal joint are 

 two subequal rami ; the inner is furnished with a series of spines 

 on the inner margin, corresponding to and continuous with 

 those upon the basal joint. The outer ramus is clean and slightly 

 longer, and terminates in several cilia, which, by their close 

 approximation, generally make the outer ramus appear longer 

 than the inner. The telson reaches to about the extremity of 

 the basal joint of the terminal pleopoda, and terminates bluntly, 

 and is furnished with four or five spines or stifi" hairs, similar to 

 those on the inner margins of the pleopoda. Length of animal 

 rather more than half an inch. 



The specimen from which this description is taken was brought 

 up from a depth of 10 to 15 fathoms, in Port Kennedy, by 



