268 DISCOVERY REPORTS 



An historical account of this genus is inckided in Beddard's report (18846, pp. 2-4), 

 and for this reason I shall not refer to its earlier history. 



The characters of the genus may be defined in the following terms : 



Body depressed, flattened and usually broad, with the first two thoracic somites fused 

 with the head, the sides of which are fused with the forward lateral extensions of the 

 second somite ; the tergum and coxal plates of the last (eighth) thoracic somite never 

 complete, usually wanting ; the tergum of the seventh thoracic somite may also be in- 

 complete. Coxal plates of the first three free thoracic (3rd-5th) somites always separated 

 from them by sutures ; sometimes, in addition, those of the fourth, or those of all the 

 remaining somites are also separated from them by sutures. First abdominal segment 

 without pleural plates, sometimes partially fused with the tergum of the seventh thoracic 

 somite; second and third abdominal segments free, with either short or long pleural 

 plates; last two fused with telson to form a large terminal segment. Mouth-parts 

 normal ; antennule with four and antenna with five peduncular joints ; each with a 

 multi-articulate flagellum. Second pair of thoracic appendages of both sexes and third 

 pair of adult male modified into a prehensile organ, the dactylus folding back upon the 

 greatly dilated propodus ; last thoracic appendage usually smaller than the others, and 

 sometimes modified in the adult male. First three pairs of pleopods natatory, consisting 

 of protopodite, exopod and endopod, the two latter fringed with long plumose setae; 

 endopod of male prolonged into a long penial filament; fourth and fifth pleopods 

 branchial. Uropods lateral in position, lamellar and usually biramous. 



Caiman (1920, p. 299), in his paper on the new species S. beddardi, suggested that it 

 might form a distinct genus with the allied species S. laiifrom, Miers, and further that 

 a regrouping of the remaining species might be advisable. In his suggested classification 

 which is based on the form of the uropods and of the terga of the posterior thoracic 

 somites, he divides the species into three groups : 



(i) A group containing S. latifrons and S. beddardi, in which the endopod of the 

 uropod is absent, and the tergum of the last (eighth) thoracic somite persists as a pair of 

 minute lateral sclerites each with a coxal plate separated by a suture. In both the 

 remaining groups the uropod bears an exopod and an endopod. 



(ii) A group containing the six AustraUan species, S. tuberctdata, Grube, S. aiistra- 

 liensis, Beddard, S. longicaudata, Beddard, S. elongata, Beddard, S. mimita, Beddard, 

 and S. pallida, Beddard, which Beddard (1884Z), pp. 66 and 81) states form "a well- 

 marked subdivision of the genus", together with S. bakeri, Chilton. 



(iii) A group, represented by S. paradoxa, Fabricius, containing all the remaining 

 species. 



The following points result from a consideration of these groups as they stand : 



(i) That the absence of the endopod of the uropod is a character which is no longer 

 peculiar to the members of group (i). It is absent from the uropod of S. platygaster, 

 n.sp., a species which is in no other way closely related to members of this group. 



(2) That if this character (absence of endopod) is disregarded the only character 

 separating members of this group from those of group (iii) is the presence of small 



