REPORT ON THE ISOPODA. 103 



The frontal margin of the head is broad and truncated ; it is not excavated by a 

 semicircular notch as in so many other species. 



The first four. thoracic segments are subequal in length, they are convex posteriorly, 

 and flatter anteriorly ; their surface, as of the body generally, is quite smooth and free 

 from tubercles or spines. In the case of the last three of these segments, the epimera 

 are furnished on each side of the body with a long spine, which is directed outwards 

 approximately at right angles to the longitudinal axis of the body. 



The fifth, sixth and seventh segments of the thorax, like the four anterior, possess a 

 long spine upon each epimeron ; each of these segments has in addition a lateral spine on 

 either side situated about half way between the dorsal median line and the ventral margin 

 of the tergum, extending .outwards from the side of the body in a direction more or less 

 parallel to that of the epimeral spine. 



Of the three free segments of the abdomen two are furnished with a long lateral spine, 

 which is absent from the middle one of the three. 



The caudal shield is very convex and terminates in the median dorsal line in a short 

 curved spine, as in so many other species of this genus. The lateral margin of the caudal 

 shield is beset with a series of somewhat curved spines which are situated at equidistant 

 intervals from each other ; they correspond in position to the spines upon the first and 

 third of the abdominal segments ; the lateral margin of the caudal shield terminates in a 

 longish flattened spine on either side, as iu Arcturus anna. 



On either side of the dorsal median line, and close to it, is another row of spines which 

 runs from end to end of the caudal shield. 



The antennules (PI. XXV. fig. 2) are of considerable length proportionately to the 

 antennae ; each is made up of four joints which decrease progressively in length from the 

 first to the third ; the fourth joint, which bears the olfactory hairs, is about equal in length 

 to the first. 



The antennse (fig. 3) have two extremely short basal joints, of which the second bears 

 a longish spine on the dorsal side, close to its articulation with the succeeding joint ; the 

 third and fourth joints are of equal length, and four or five times as long as the basal 

 joints taken together ; each has a similar spine at its distal extremity ; the fifth joint is 

 both longer and narrower than the preceding joints, it has no terminal spine ; the 

 flagellum is extremely short, about one-third as long as the terminal joint ; it is composed 

 of two segments only, the distal being the longer. 



Another characteristic of this species is the great length of the thoracic appendages ; of 

 the four anterior pairs the first are as usual shorter than the rest and subcheliform ; the 

 second pair has the two proximal joints moderately short and subequal; the first joint 

 has a long spine similar to those upon the thorax placed near to its articulation with the 

 body ; the third joint is as long as the two basal joints taken together, its inner margin 

 is fringed as in other species with numerous long hairs ; the fourth joint is of entirely 



