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



head, reach to auy length; the antenna) are also considerably shorter relatively than in 

 either of the two other Kerguelcn Arcturi. 



The nearest affinities of this species are with Miers' Arcturus coppingeri and with 

 Arcturus americanus, from both of which it differs in the absence of the posterior spines 

 upon the caudal shield, in the presence of a pair of spines upon the head, in the shortness 

 of the antennae and in the very short truncated caudal shield. 



The specimen measures about 13 mm. in length : the anterior region of the thorax is 

 extremely broad, as is often the case in the females of this genus (for instance in Arcturus 

 spinosus, see p. 89). 



The head is extremely short, and the large and prominent eyes are not far removed 

 from its anterior margin ; on the dorsal surface, between the eyes, are a pair of stout 

 spines directed upwards but diverging from each other; behind these again, and 

 corresponding to them in position, are a pair of very short spiny tubercles. 



The thoracic segments gradually increase in length up to the fourth; there is not, 

 however, much difference in this respect between the third and fourth. In the first 

 three segments the dorsal surface is ridged and covered with strong blunt tubercles, of 

 which two, one on either side of the median line, are particularly marked, at any rate in 

 the second and third segments ; in these segments also a prominent process overhangs 

 the articulation of the appendages. The fourth segment is much less strongly ridged 

 than the preceding ; it is divided by superficial transverse furrows into three areas of about 

 equal dimensions, the anterior is smooth and the middle area sparsely tubercnlate 

 ventrally; between the two is a roughened tuberculate area which overhangs the articula- 

 tion of the limbs ; the posterior region of the segment corresponds to the ridge on the 

 anterior segments. The posterior thoracic segments are ridged and covered with rounded 

 tubercles which are smaller and not so pointed as those of the anterior segments. The 

 abdominal segments and caudal shield are closely beset with similar tubercles; the 

 caudal shield is remarkably short, being hardly longer than the three free abdominal 

 segments^ it ends in a blunt somewhat upturned extremity; dorsally and laterally are 

 a pair of pointed short spines. 



The antennse measure 9 mm. in length ; the two distal joints are elongated and 

 subequal, and like the proximal joints beset with numerous hairs and spines ; the flagellum 

 is shorter than the distal joint of the peduncle and is only three-jointed, as in Astacilla. 



The proximal joints of all the thoracic appendages are roughened and tubercular 

 (figs. 3, 4). 



Station 149e, off Kerguelen Islands, January 21, 1874. Off Cape Maclear; depth, 

 30 fathoms. 



