288 "TERRA NOVA" EXPEDITION. 



specimens tlie proximal and distal series meet. The distal spines are thus older 

 spines than the more proximal ones (except, of course, the original proximal series). 

 M. kerguelensis is described as 10 mm. long and M. illigi as 13 mm., the latter, at 

 any rate, admittedly immature. If my suggestion is correct, the armature of the 

 telson in both these species must be regarded as evidence of their hnmaturity and 

 not as a valid specific character. Both these species are thereby brought into 

 much closer relation to M. posthon, but their real affinity cannot be established 

 until larger specimens are examined. As far as can be seen at present, M. kerguelensis 

 is distinguished by the much shorter antennal scale which is only very slightly 

 longer than the antennular peduncle. In the young specimen here ascribed to 

 M. fostlion, the proportions of the antennal scale are as in adult specimens of that 

 species. 



M. illigi is further distinguished from M. posthon, according to Zimmer, by the 

 larger and more produced rostral plate, by the small upper and large lower spines 

 on the basal joint from which the scale springs, and by the greater comparative length 

 of the inner uropod. In the last character my young specimen of M. posthon agrees 

 with M. illigi. In the other two characters it agrees with adult 31. posthon. In 

 view, however, of Hansen's demonstration that these characters are very variable 

 and cannot be relied on as specific marks, it would appear that ilf . illigi is founded 

 on a young specimen of M. posthon. I think this is highly probable, and provisionally, 

 at any rate, I would refer 31. illigi to the synonymy of 31. posthon. 



31. hanseni, the third of the new species of 31ysidetes described by Zimmer, 

 appears to be distinguished by the much shallower cleft of the telson and its round 

 apical lobes, and by the absence of spines on the inner margin of the inner uropods. 



Distribution. — 31. posthon has been obtained by both British Antarctic 

 Expeditions, by the " Belgica," the " Gauss," and the Swedish expedition. I have 

 seen specimens also in the Paris Museum which were obtained by Dr. Charcot during 

 his 1909 expedition. The species is therefore circumpolar in range. 



12. 31ysidetes hrachylepis, sp. nov. (PL I, figs. 1-2.) 



Occurrence. — Antarctic, Station 331. One adult female, 17 mm. 



Description. — The single specimen is much mutilated. There remain no 

 appendages except the inner uropod of one side. Most of the setae from the antennal 

 scale and most of the spines from the telson are broken off, and the specimen is 

 generally fragmentary. But the essential characters of the rostrum, ej^es, antennal 

 scale, and telson can be made out, and these are so distinct that it is possible to 

 institute a new species with some degree of confidence. 



Carapace produced anteriorly into a moderately long triangular plate extending 

 forward as far as the distal margin of the eyes, angle of the apex acute, but the tip 

 bluntly rounded. 



