REPORT ON" THE ISOPODA. 113 



and form a cephalic shield, is flattened in front, but convex laterally and behind. The 

 frontal margin projects as a short sharp rostrum ; behind the insertion of the antennary 

 organs is a triangular ocular lobe pointed in front ; it has no trace of any optic 

 structures ; behind this again is another shorter, triangular, pointed process ; more 

 posteriorly the lateral margins of the cephalic shield are convex outwards. 



The free thoracic segments diminish gradually in breadth, but increase in length 

 up to the fifth ; the sixth is not only narrower but shorter than the fifth. They are 

 all furnished with very minute epimera, those of the first segment are larger and 

 project anteriorly in the form of a short spine. The lateral margins of all but the 

 first two segments are furnished with a short spine very broad at its base, which is 

 situated about half way between the articulation of the limbs and the anterior margin 

 of the segment ; in the sixth (and last) segment of the thorax this spine is almost 

 obsolete. In the ventral surface of the thoracic segments is a median spine. 



In the female the first four of the free thoracic segments have ovigerous lamella?. 



Of the abdominal segments the first pair are subequal, but diminish gradually in 

 breadth ; they are furnished with small epimera, terminating in a pointed extremity 

 and directed backwards. 



The terminal segment of the abdomen equals in length any four of the anterior 

 abdominal segments ; it is cylindrical in form, becoming gradually wider towards the 

 extremity ; it terminates in a truncated straight posterior margin, and in the middle 

 line in a short oval prolongation. 



The antennules are stouter as well as longer than the antennae ; they are about 

 as long as the cephalothoracic shield and the first segment of the thorax taken 

 together. The basal joint is long and stout, the second joint is very much 

 shorter, the third and fourth shorter still ; from the last joint of the peduncle arise the 

 two flagella, of which the outer is longer as well as stouter than the inner ; the outer 

 flagellum is made up of ten joints, of which the first is very much the longest ; 

 it diminishes gradually in width towards the extremity ; the inner flagellum has four 

 or five narrow elongated joints. 



The antennse have a five -jointed peduncle and a flagellum about as long as the last 

 two joints. The first joint of the peduncle is short, the second long, with a short, 

 cylindrical, setose exopodite articulated at its extremity ; the third joint is very short, 

 the fourth and fifth long and subequal. 



I have not a sufficient amount of material at my disposal to give an accurate 

 account of the mouth appendages. 



The chelse are not remarkable in any way except for the absence of an exopodite ; 

 they appear to be perfectly similar in both sexes, and agree very closely with those of 

 the genus Sphyrapus (female), &c. The first joint is very much stouter than any of 

 the succeeding joints ; the second is short and narrow and bears a spine on the inner 



(ZOOL. CHALL. EXP.— PART XLVIII. — 1886.) Ebb 15 



