REPORT ON THE ISOPODA. 75 



The cephalic shield is almost triangular in shape, from the great development of the 

 ocular prominences and a large median backwardly projecting spine ; the rostrum is long 

 and slender, and reaches nearly as far as the distal end of the second joint of the posterior 

 antennae ; the anterior margin of the cephalic shield is thickened into a ridge, which 

 bifurcates at the edge, the two branches being directed forwards and enclosing a deep 

 cup-like space ; shortly before the bifurcation a small spine-like process is given off 

 anteriorly. 



Thorax. — The epimera are short, gradually increasing in length up to the sixth pair ; 

 the first epimera are entire as in the other Australian species, and not divided by any 

 transverse suture ; at the u^jper extremity is a short ridge on either side, which extends 

 for about one-sixth of its length parallel to the anterior margin of the epimeron. 



In the three succeeding epimera the curvature of the outer margin is very slight, 

 which gives them the appearance of being abruptly truncated. The fifth epimera are more 

 sickle-shaped, since the outer is inclined at a smaller angle to the posterior margin ; the 

 outer margin of the sixth epimera is concave. 



The terga of the thoracic segments, with the exception of the first and the two last, 

 have a median hooked spine directed upwards and Imckwards ; these increase slightly in 

 size from before backwards ; the antero-posterior diameter of three anterior free thoracic 

 segments is about the same ; the fourth is not more than one-fifth as wide as the 

 preceding segments, and the tergal portion of the last thoracic, as in other Australian 

 species, has entirely disappeared. 



Abdomen. — The epimera of the second and third abdominal segments only reach as 

 far as the margin of the caudal shield ; they are equal in length. The terga of the three 

 segments are furnished with a spine like that in the thoracic segments ; these spines, 

 which are rather smaller than those on the thorax, increase in size from before backwards. 

 The sterna of these segments are produced into a long median spine, which is larger in 

 the first segment than in the two succeeding ones. 



The caudal shield in the female measures 5 '5 mm. in length, and is therefore rather 

 more than one-third of the length of the entire animal ; it is irregularly hexagonal in 

 outline, and keeled ; the extremity is notched ; the uropoda are attached about half way 

 down ; just below and to the inside of the spine-like process which covers the articulation 

 of the uropoda is a minute flattened spine on either side. 



The two pairs of antennce are approximately of the same length. The basal joint of 

 the first pair (PL VIII. figs. 7, 8) has three strong tubercles on its upper surface ; the 

 second joint has a stout tubercle on the posterior margin projecting backwards ; the 

 filament has twenty-four joints, each of which is furnished with two sensory hairs (fig. 8), 

 as in Serolis australiensis. 



In the second pair of antennae (PI. VIII. fig. 6) the fifth joint is very much enlarged ; 

 it is not quite so long as the preceding joint, but wider; the filament is short, being 



