Chilton. — The New Zealand Species of Elasmopu*. 321 



So far as the New Zealand forms are concerned, the characters which 

 seem most useful for distinguishing the species are whether the pleon is 

 carinated or not, the character of the carination when present, and the 

 shape of the second gnathopods in the male. The second gnathopoda are 

 usuallv much more largely developed in the males than in the females, 

 and their distinctive characters appear to be attained only in fully deve- 

 loped males, so that the particular form of gnathopoda may vary consider- 

 ablv owing to the age and development of the animal ; and from what 

 has been stated below it seems probable that in one species there are two 

 forms of gnathopoda in the adult males, apparently similar to what has been 

 described by Mrs. E. W. Sexton in the case of Jassa falcata (Montagu). 

 In these cases it is, of course, difficult to decide whether we are dealing 

 with one species with two forms of male, or with two different species in 

 which the females are practically indistinguishable although the males are 

 different. In the following list I have treated the forms as belonging to 

 separate species, except in the one case where the differences between the 

 males are confined to the second gnathopoda. 



Elasmopus subcarinatus (Haswell). Figs. 1-6. 



Megamoera subcarinatus Haswell, 1879, p. 335, pi. 21, fig. 4. Moera 

 petrieiG. M. Thomson, 1882, p. 236, pi. 18, fig. 3; Chilton, 1883, 

 p. 82, pi. 2, fig. 4a. Moera subcarinata Chilton, 1884, p. 230 ; 

 1884a, p. 1039 ; and 1885. p. 368. Elasmopus subcarinatus 

 Stebbing, 1906, p. 441 (with synonymv) ; 1910a, pp. 602 and 

 643; 1910b, p. 457: Walker, 1904, p. 275, pi. 5, fig. 34; 1909, 

 p. 335. 



The history of this species is briefly as follows : It was described in 

 1879 by Haswell from specimens obtained at Port Jackson, where it is 

 common. He described only the male, and says the pleon is " dorsally 

 carinate, the carina projecting posteriorly in the form of a compressed tooth."' 

 though it is really bicarinate, each carina ending in a tooth. In 1882 Thom- 

 son independently described the species under the name Moera petriei from 

 two specimens from Stewart Island, New Zealand, correctly describing the 

 " fourth segment of the pleon produced into two acute spines [teeth] 

 on its postero-dorsal border " ; his description applies to the male only. 

 Shortly afterwards I obtained specimens in Lyttelton Harbour that I 

 identified with Maera petriei Thomson, and in 1883 I described and figured 

 the second gnathopod of the female, and at the same time pointed out that 

 the males from Lyttelton differed from the description given by Thomson 

 in the shape and hairiness of the second gnathopoda. A little later I col- 

 lected in Port Jackson specimens that I had no hesitation in identifying 

 with Megamoera subcarinata Haswell, the type of which came from that 

 locality. The females were quite like those from Lyttelton which I had 

 assigned to Maera petriei, and the males agreed with the description given 

 by Thomson, thus differing slightly from those I had obtained at Lyttelton. 

 Accordingly I united the two species, and drew attention to the fact that 

 there appeared to be two forms of the male (1884a, p. 1039, and 1885, p. 368). 

 The ''Challenger" Expedition obtained two specimens from Station 168. 

 off New Zealand, and in 1888 Mr. Stebbing, after comparing these with 

 specimens of Maera petriei sent by me from Lyttelton and with Thomson's 

 description, withdrew the specific name persetosus, under which he had 

 commenced to describe them as a new species, and assigned the " Challenger "' 



11— Trans. 



