■REPORT ON THE ISOPODA. 55 



suture, and uj^on which two transverse furrows mark the boumlar)- l^etween the several 

 segments of which it is composed. The lateral portions of the sterna of the three segments 

 are at first fused together, but become separate just before the attachment of the append- 

 ages ; and a triangular plate with the apex directed posteriorly, lies between the median 

 and lateral portions of the sternum of the sixth segment. 



Abdomen. — The first abdominal segment has as i;sual no epimera ; its width is about 

 double that of the preceding thoracic segment ; the second and third abdominal segments 

 are long and well developed, and terminate in a somewhat bifid extremity, the inner limb 

 of the bifurcation being considerably longer than the outer (figs. 1, 2). The sterna of the 

 three free abdominal segments are shown in fig. 2 ; there is a short median backwardly 

 projecting tubercle, longer in the second and third than in the first ; this is continuous 

 with a lonoitudinal rida;e which is crossed at right anoles by another ridse. The male and 

 female specimens, as already mentioned, show hardly any difterences in the conformation 

 of thefee abdominal sterna ; in the female the antero-posterior diameter is somewhat less, 

 and the median tubercle somewhat more pronounced than in the male. 



The caudal shield, which is liroader than long, has a somewhat pentagonal contour 

 with rounded angles ; the uropoda are attached about half way down the side, the 

 posterior extremity is notched and rather turned up ; there is a median longitudinal keel, 

 and on either side a short flat spine near the lateral margin, and on a level with the 

 attachment of the uropoda ; the surface between the keel and these spines is almost flat, 

 but is strongly bent downwards ; the length of the caudal shield in the male is 1 7 mm. , 

 almost half that of the rest of the body, its breadth 21 mm. 



AjJjjendages. — The antennce are almost exactly of the same length. The first pair of . 

 antennse has four joints and a terminal filament made up of thirty-one joints, and equal 

 in length to the first four joints. 



The basal joint is oval, with a truncated distal extremity; the second joint slightly 

 longer, with a straight outer and convex inner margin ; the third joint is half again as 

 long as the second and about half its width; it is cylindrical in shape; the terminal joint 

 is about one-third of the length of the preceding joint, and of the same shape. 



The second pair of antennas have six joints and a short terminal filament ; the 

 sixth joint is the longest, the thml is slightly longer than the fourth; the two basal 

 joints ai'e small, especially the second, which only occupies one side of the antennse, 

 on the other (inner) side the first joint articulates directly with the third ; on the fourth, 

 fifth, and sixth joints are a series of ridges running transversely to their long axes, 

 and bearing bunches of fine hairs. 



The mandibles are as usual asymmetrical ; the left hand one has a projecting chisel- 

 shaped process which is wanting in the right hand one. 



The maxillcs are like those of other species ; the anterior pair lias nine or ten 

 curved spines upon the cutting edge, the most anterior of which appear to be the largest. 



