REPORT ON THE ISOPODA. 101 



The head bears dorsally two pairs of long spines, the anterior pair being in advance of 

 the posterior pair which are behind the eyes ; there are also a few short spines borne on a 

 ridge which occupies the posterior region of the head and is continuous with the convexities 

 which are topped by the hinder pair of spines ; the lateral margin of the head is not a 

 straight line at right angles to the longitudinal axis, but the lower portion is cut away 

 as in Arcturus purpureus, &c, and meets the upper portion at an obtuse angle. 



The four anterior thoracic segments are subequal, and each has a posterior ridge 

 bearing a number of longer and shorter spines. On the first segment the spines upon 

 the posterior ridge are disposed as follows : — there are a pair of minute tubercles, one on 

 either side of the median line corresponding in position to the spines upon the head ; 

 laterally are two long spines equidistant from each other and from the median tubercles ; 

 the lateral margin of the tergum is prolonged into two outwardly and downwardly- 

 directed spinous processes, of which the anterior is the longer. In front of the posterior 

 ridge, and about half way between it and the anterior margin of the segment, is a shorter 

 ridge which bears four small blunt tubercles, the two inner ones corresponding exactly 

 in position to the median tubercles of the posterior ridge. On each of the three 

 succeeding segments the number and position of these tubercles is identical ; on each of 

 these segments the posterior ridge, like that of the first thoracic segment, has two long 

 spines upon each side of the body ; the third and fourth segments have in addition 

 another spine upon each side placed behind and between the two lateral spines ; these 

 are also present in rudiment on the two anterior segments, and in fact increase pro- 

 gressively in size from before backwards. 



The margin of the epimera is prolonged into three spines, which are extremely short and 

 inconspicuous in the second thoracic segment ; in the third segment the two posterior 

 spines are of considerable length ; in the fourth the middle one is very long, while the 

 posterior spine is broadened out into a long plate bearing secondary spines along its pos- 

 terior edge and almost meeting its fellow on the opposite side ; these processes are closely 

 pressed against the ovigerous lamellae, and their function appears to be to support them. 



Each of the three posterior thoracic segments has two or three long spines on either 

 side ; the epimera are large and terminate inferiorly in two stout spines inclined out- 

 wards and downwards, and at an acute angle with each other. 



The two anterior abdominal segments each consist of two regions, a narrower anterior 

 and a swollen posterior portion, the former is smooth, the latter beset with spines and 

 tubercles ; on the first segment are two particularly long spines, one situated close to 

 the ventral margin of the tergum just in front of the anterior extremity of the uropoda, 

 which abut against the hinder region of this segment ; exactly above this is another spine 

 of equal length ; on the second abdominal segment is a long spine on either side, placed 

 much more dorsally than in the anterior segment. The third abdominal segment is 

 shorter than the other two, and is closely fused with the caudal shield ; it is roughly 



