REPORT ON THE ISOPODA. 37 



Astrurus crucicauda, F. E. Beddard (PL V. figs. 9-19). 



Astrurus crucicauda, F. E. Beddard, Proc. Zool. Soc. Lond., 1886, pt. i. p. 100. 

 This, the only species of the genus, is represented by a very considerable number of 

 specimens dredged in shallow water off the shores of Kerguelen ; it is a small species, the 

 largest individuals only measuring 4 mm. in length. 



The body is oval in general outline, the anterior region of the thorax being of greater 

 width than the posterior region, the surface of the body is abundantly furnished with 

 spines ; the head is narrower than the succeeding segment of the thorax, it is prolonged 

 in front into two long slightly divergent processes, which are rather longer than the head 

 itself. Behind this bifid rostrum on either side the margin of the head is incised for the 

 insertion of the antennules ; posterior to the insertion of these, the margin of the head is 

 prolonged laterally into a process which is rather wider at its free extremity than at the 

 base ; the general appearance of this process is very like that of the " stalked" eyes of 

 the allied genus Munna ; in the interior was an orange coloured substance which is of 

 the same tint as the partially disclosed eye-pigments in many Crustacea ; the surface of 

 the lateral process is, however, beset with numerous spines, and its extremity ends in a 

 particularly long spine. 



The four anterior thoracic segments are of equal or nearly equal length ; their breadth 

 gradually increases up to the third, which is the widest ; the median region of each 

 segment, which is equivalent to nearly the whole of it, is convex and densely covered with 

 spines, the lateral margins of the segments are prolonged into narrow spiny processes of 

 considerable length, which are themselves covered with spines. In the first two segments 

 these spines follow the general curvature of the segments themselves and are directed 

 forwards ; in the third segment they are directed at right angles to the longitudinal axis 

 of the body, and in the fourth segment slightly backwards. The length of the spines is 

 about one-third of the diameter of the body. 



Of the three posterior segments of the thorax the first two are subequal in length and 

 shorter than the anterior segments, they decrease gradually in width ; the seventh 

 thoracic segment is equally long but narrower again. 



The lateral margins of these segments are not furnished with the long processes of 

 the anterior segments of the thorax, only in the fifth and sixth segments one of the small 

 spines which fringe the body is elongated to a greater extent than the rest ; on the seventh 

 segment this spine is hardly larger than the surrounding ones. 



The abdominal shield is constricted anteriorly, and there is a distinct free abdominal 

 segment ; the middle portion is oval ; behind the articulation of the uropoda it becomes 

 suddenly narrower, and terminates behind in the peculiar fashion indicated in fig. IS of 

 PI. V.; the posterior extremity is formed by four somewhat curved spines arranged with 

 reference to each other like the arms of a starfish, the fifth arm being as it were widened 

 out at the base of attachment to the abdominal shield. The surfaces of this region of 



