REPORT ON THE ISOPODA. 95 



Both specimens are males, the larger measures 13 mm. in length, the antennae being 

 20 mm. in length. 



Unlike so many other deep sea species, Arcturus spinifrons, has no development of 

 spines upon the carapace with the exception of a single pair on the head ; the body is, 

 however, very tuberculate. 



The anterior margin of the head is notched in a semicircular fashion ; the anterior 

 part of the head is smooth save for two long spines which lie between the eyes ; the 

 posterior part of the head is convex and divided by furrows into three prominences, one 

 median and two lateral, which are closely covered with tubercles. The lateral margin of 

 the head, as in Arcturus anna, is excavated by a ventral semicircular notch. 



The four anterior thoracic segments are equal in size. Each has a posterior ridge 

 which widens out laterally ; the anterior margin of the ridge is concave ; the lateral regions 

 are separated by a furrow from the median and both are densely covered with tubercles ; 

 the epimera are short and inconspicuous, and appear to be smooth or at least not so rough 

 as the terga. 



The anterior concave margin of the ridge closely embraces an oval convexity which 

 lies close to the anterior margin of the segment ; in the first segment this convexity 

 is divided by a tranverse line of division into two equal halves, each of which bears 

 a single row of tubercles ; these regions are also densely tuberculate in the following 

 segments. 

 \ The fourth thoracic segment has a row of short tubercles arranged in a semicircle with 

 the concavity directed backwards upon the ventral surface ; the dorsal oval convexity is 

 not so large as in the two preceding segments, and has only two tubercles, one at either 

 extremity. 



Of the three posterior segments of the thorax, the first is the largest, the second and third 

 being smaller and subequal ; each of the segments is traversed by a strong ridge which is 

 covered with tubercles ; the first of the segments has a number of short tubercles 

 scattered over the ventral surface, and the two succeeding segments are ridged in the 

 same region. 



The segments of the abdomen are comparatively smooth, being only slightly roughened 

 laterally ; the caudal shield is smooth with the exception of the lateral margins which are 

 serrate ; it terminates in a short median spine. 



The antennules extend half way along the third joint of the antennae. 



In the antennae the terminal joint is the longest, measuring 6 mm., the penultimate 

 joint measures 5 mm. ; the flagellum is of about half the length of the terminal joint. 



The thoracic appendages are roughened and tuberculate on the proximal joints. 



The uropoda bear a single median longitudinal row of tubercles. 



Station 174c, off Kandavu Island, August 3, 1874; lat. 19° 7' 50" S., long. 

 178° 19' 35" E. ; depth, 610 fathoms; bottom temperature, 39° F. ; coral mud. 



