REPORT ON THE ISOPODA. 91 



Arcturus anna, F. E. Beddard (PI. XIX. figs. 1-5). 



Arcturus anna, E. E. Beddard, Proc. Zool. Soo. Lond., 1886, pt. i. p. 107. 



A single female example of this species was obtained in deep water off the east coast 

 of South America. 



The specimen measures 37 mm. in length exclusive of the antennae, which are very 

 long, measuring altogether 64 mm., with the exception of the extreme tip which was 

 broken off. 



The head is excavated in front and bears two large lateral eyes of a somewhat 

 triangular form with rounded angles ; it is sharply marked off, at least laterally, from the 

 anterior segment of the thorax. 



The anterior lateral margin of the head is notched ventrally. 



The first four thoracic segments are subequal in length ; each is traversed by a ridge 

 which dorsally is narrow and occupies only the posterior portion of the segment ; laterally 

 the ridge upon each segment expands in width and comes to occupy the whole of its 

 superficies ; in this region the ridge upon the segment is not uniform, but traversed by 

 several shallow furrows which divide it into two or three rounded emminences. At the 

 extreme lateral margin, just before the articulation of the epimera, is a longish stout spine 

 incbned more of less at right angles to the longitudinal axis of the body, and slightly 

 bent downwards ; behind are one or two shorter spines along the postero-lateral border ; 

 the epimera which are short and not visible on a dorsal view of the animal, are likewise 

 furnished along their free border with one or two spines ; these are only conspicuously 

 developed upon the last two of the segments, especially upon the last, where one of the 

 spines equals in length the spine upon the terga, and lies directly beneath it. Each of 

 these first four segments has another slight ridge upon the dorsal surface, placed about 

 half way between the posterior ridge and the anterior boundary of the segments ; this 

 ridge is thicker upon the first thoracic than upon any of the succeeding segments ; 

 laterally the anterior ridge of each segment disappears and does not come into contact 

 with the widened portion of the posterior ridge. 



The three posterior thoracic segments are together equal in length to the third and 

 fourth ; of these the first is distinctly the largest. Each is ridged posteriorly, and the 

 ridge widens out laterally to occupy the whole of the segment ; it is here divided by a 

 suture passing obliquely from above downwards and backwards into two convex areas ; 

 the lower convexity, which is the epimera, bears a stout spine which projects over the 

 articulation of the limbs ; the epimera are not visible on a dorsal view ; in the most 

 anterior of the three segments the epimera has in addition an equally long spine placed 

 in front of the other, and directed forwards instead of outwards ; each segment also has 

 on either side a short lateral spine corresponding to those on the preceding segments 

 but considerably smaller. 



