DESCRIPTION OF SPECIES 



305 



Description. The body (Fig. 9) is broadly oval with a median keel ; the male, the 

 largest specimen of which measures 

 7-5 mm. in length and 6-25 mm. in 

 greatest breadth, is slightly broader in 

 proportion to its length than is the 

 female: the latter measures 7 mm. in 

 length and 5-5 mm. in breadth. The 

 colour and markings of the body appear 

 to be very variable. 



The head is about twice as broad as 

 long, shield-shaped in outline, with a 

 narrow transverse ridge close to its 

 anterior margin which extends laterally 

 to the sides of the cephalosome. The 

 portion of the head between the eyes is 

 convex, with a strong median dorsal 



Fig. 9. 



Serolis exigua, Nordenstam, (J : x 12. 



keel which is continued backwards as a spiniform process to about the middle of the 

 third (first free) thoracic somite. The eyes are large, about half the length of the head, 

 reniform in shape and containing black pigment. 



Each of the third to the seventh thoracic somites has its posterior margin produced 

 into a median dorsal spiniform process ; those of the third, fourth and fifth somites are 

 larger than those of the following somites, but are smaller than the corresponding pro- 

 cess of the head: these processes are not so well developed in the female. The coxal 

 plates of the third to the seventh thoracic somites are well developed, those of the third, 

 fourth and fifth are separated from their respective somites by sutures. In the male the 

 coxal plates of the seventh thoracic somite do not extend backwards quite as far as the 

 pleural plates of the second abdominal segment; in the female they are considerably 

 shorter. 



The abdomen (Fig. 9) consists of three free segments and a large terminal one ; each 

 of the three free segments is slightly keeled and has a short median dorsal spine corre- 

 sponding with those of the thoracic somites. The pleural plates of the third abdominal 

 segment extend backwards beyond those of the second to a point level with the base of 

 the uropod ; the outer margins of both the coxal and pleural plates are sparsely fringed 

 with hairs and short hairs are also present on their posterior margins. 



The terminal segment is roughly five-sided, with the angles rounded. A median 

 dorsal keel extends to the posterior extremity of the segment, but is more pronounced in 

 the anterior half. On either side of this keel, lying midway between it and the lateral 

 margin of the segment, is a lateral carina which extends nearly to the posterior margin 

 of the segment ; a secondary carina arises half-way along each of the lateral carinae and 

 passes forwards and outwards to the lateral margin of the segment. 



The antennule (Fig. 9) is very deUcate, and consists of a peduncle of four joints and a 

 flagellumof eight ; the first peduncular joint is broad and geniculate, the second sub-equal 



