PONTOGENEIIDAE 205 



animal, small specimens having two teeth as in the Challenger type, larger ones 7-10 

 teeth. On this account no doubt has hitherto been expressed as to the identity of the 

 Australasian and Antarctic specimens, and the "species" has been credited with a wide 

 distribution. It should be noted that not a single large or small specimen with numerous 

 teeth has yet been recorded from the Australasian region. 



The examination of the Discovery collection has led me to doubt both the variability 

 and the wide distribution, and to believe that two distinct species have been united. 



Stebbing (1888, pi. lxxviii) gives a general habitus figure of the Australian serrati- 

 cauda showing on the head below the antero-lateral rounded projection, and separated 

 from it by a slight indent, a very shallow "cheek" 

 with a rounded post-antennal corner. Stephensen 

 (1927, p. 339) in commenting on Auckland Island 

 specimens says "the outline of the face is as shown 

 by Stebbing ... thus there is no projecting post- 

 antennal corner". This is a very welcome corrobora- 

 tion of Stebbing's accuracy. No other author has a fa 

 referred to this point. Chilton's fig. 21 (1912) stops Fig ^ Schroderia gracilis (Pfr.). Head 

 just short of including the decisive feature. f : a. Adult, b. Young (6 mm.). 



But if Stebbing's and Pfeffer's figures are compared 

 it will be seen that they do not agree. Pfeffer shows a deep cheek with a quadrate though 

 not projecting post-antennal corner. As I have elsewhere remarked Pfeffer had a very 

 accurate draughtsman, though in the case of S. gracilis he has omitted the serrations on 

 the pleon segment 3 and on the anterior margin of the cheek. But it is quite evident that 

 the specimens here examined, from the type locality, conform with those Pfeffer had. 

 I am thus led to conclude that there is an Antarctic form with deep, serrated cheeks 

 and numerous serrations on the margin of pleon segment 3 ; and an Australasian form 

 with shallow, entire cheek and a bidentate postero-inferior corner on pleon segment 3 . 

 These two forms ought certainly to be recorded separately, and I am of opinion that 

 both should be given specific rank. Stebbing's serraticauda thus becomes the second 

 species of Schraderia. 



Owing to the unfortunate overlooking of this diagnostic character all the Antarctic 

 records are open to doubt, though one feels fairly safe in assuming that those given 

 above, with query marks against them, will on re-examination be found to apply to 

 gracilis. 



The references to serraticauda are as follows : 



Stebbing, 1888, p. 920, pi. lxxviii; 1906, p. 362. 



? Chilton, 1909, p. 627. 



Stephensen, 1927, p. 339. 



The integument in gracilis is minutely shagreened, with minute scattered pits, from 

 which an occasional seta arises. 



Distribution. South Georgia. Probable but requiring confirmation: Graham 

 Land; South Orkneys; Ross Sea area. 



