334 DISCOVERY REPORTS 



26. Serolis yongei, Hale. 



S.yongei, Hall, 1933, pp. 560-1, i text-fig. 



Hale's description of this species is extremely short ; it is based on two small specimens 

 collected outside Trinity Opening, Low Isles, during the Great Barrier Reef Expedition. 

 Through the kindness of Dr Caiman I have been able to examine these specimens, and 

 as a result of my observations am able to amplify the original description in a number 

 of points. 



Diagnostic characters. The larger specimen, which is a female in the non-breeding 

 condition with the four pairs of brood plates well developed, measures 2-9 mm. in 

 length and 2-5 mm. in greatest breadth. The shape of the body is described as "wide, 

 pyriform, dorsal surface almost smooth with shallow pitting". 



The head is broader than long, about the same width anteriorly as at the level of the 

 eyes, slightly narrower between these two levels; the anterior margin is excavated on 

 either side of a fairly long rostrum for the reception of the antennules. The antero- 

 lateral margins of the head are not completely united with the forward lateral extensions 

 of the second thoracic somite, which is here, as in all species of Serolis, fused with the 

 head. The head is roundly convex between the eyes, which are large and are situated 

 on either side in a postero-lateral position. The eyes are reniform and contain black 

 pigment. 



The first three free thoracic somites (3rd-5th) are almost sub-equal, decreasing 

 slightly in length from before backwards ; the sixth is about half the length of the fifth. 

 The seventh thoracic somite is extremely narrow, with its tergum fused with that of the 

 first abdominal segment for some distance on either side of the median line. Hale makes 

 no mention of this important fact in the text of his paper, but he illustrates it in his 

 figure. 



The coxal plates are well developed, and those of the first three free somites are 

 separated from them by sutures (they are not fused as in Hale's figure). Those of the 

 seventh somite are not much more produced than those of the preceding somites ; they 

 extend backwards to a point slightly beyond that reached by the pleural plates of the 

 second abdominal segment, at about the level of the bases of the protopodites of the 

 uropods. 



The abdominal segments are sub-equal, with the pleural plates of the second and 

 third segments extending for a short distance beyond the broad anterior end of the 

 terminal segment ; those of the third segment are slightly the longer, and extend back as 

 far as about the level of the middle of the protopodite of the uropod. 



The terminal segment is broader than long, roughly triangular in shape, with the 

 apex directed backwards, and with the angles rounded ; it is broadest at the level of the 

 base of the uropods, and has a low median dorsal carina. The sternum of each of the 

 first three abdominal segments is produced into a median backwardly directed spine 

 which is largest on the first segment. 



The antennules and antennae have already been described. The form of the antennule 

 is given as "second joint of peduncle nearly half as long again as the fourth, and four 



