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



(•nous than tlic rest, forms the posterior boundary of the segment, and is continued along 

 the posterior margin of the epimera. In front of this is another row of tubercles, which 

 in the middle of the segment lies half way between the anterior and posterior margins ; on 

 cither side it divides into two rows, each, of wliich run close to the anterior and posterior 

 margins of the segment respectively ; in the two last thoracic segments this anterior row 

 of tubercles is not present. All the segments of the body, with the exception of the fifth 

 and sixth, the former of which, as in the other Australian species, disappears altogether in 

 the middle line, are furnished with a larger tubercle exactly in the median dorsal line ; these 

 increase in size from before backwards ; on the fifth segment (in the female specimen at 

 least) the median tubercle is wide, and flattened and quadrifid at its extremity. 



Ahdomen. — -The epimera of the second and third abdominal segments extend for a 

 very short space beyond the lateral margins of the caudal shield ; beneath, the three 

 anterior segments are prolonged into a stout siDine of unusual length {cf. fig. 3) ; the 

 spine of the first segment, which is the longest, completely covers the spine of the 

 succeeding segment ; the spines in the female apjDcar to be a little stouter than in the 

 male, for in the male the spines are all rather slender ; the diff"erences, however, are 

 insignificant and not well marked. 



The caudal shield is more or less triangular in outline, distinctly carinate and trun- 

 cated at its free extremity ; its upper surface is covered with tubercles, which have no 

 definite arrangement except for a median transverse row which crosses the central keel 

 at right angles a little below the attachment of the uropoda ; one of these tubercles on 

 either side, close to the lateral margin, is considerably larger than the rest. 



Of the Jirst pair of antennoB the two proximal joints are short, while the third, wliich 

 is the longest, measures about twice the length of the second. The joints of the filament 

 are extremely short and numerous ; there are about fifty ; each joint bears two sensor}' 

 filaments instead of the usual one (PI. VI. fig. 5). 



In the second, iKiir of antemuB the third joint has a large backwardly projecting 

 tubercle just before its articulation with the following joint as in Serolis tubercnlata ; 

 this joint is also smaller than the preceding one; the fourth and fifth joints are as usual 

 greatly elongated, and the outer margin is sinuous. A tuft of fine hairs springs from the 

 surface of each of the four elevations ; the filament consists of fifteen joints, which are 

 longer and more slender than the joints composing the filament of the first pair of 

 antennae; the upper surface of the third to the tenth joints has a row of short blunt 

 tubercles; one or two long fine hairs springs from the inner margin of each joint at its 

 anterior extremity. 



MontJi Appendages. — The mandibles, like those of Serolis jMlIida, have a large and 

 conspicuous tooth upon the posterior part of the masticatory edge ; behind this is 

 another smaller tooth; in front the margin .slopes back gradually to meet the outer 

 margin of the mandilale. 



