204 "TERRA NOVA" EXPEDITION. 



interesting results, for it is quite evident that fully adult male specimens have not 

 before been met with. _ There is a very marked sexual dimorphism in the form of the 

 second thoracic limb in this species. PL II, fig. 1, illustrates the second thoracic 

 limb of an adult male, 4 mm. in length, from S. Georgia. The appendages are about 

 twice as long as the body of the animal, and lie folded between the remaining 

 thoracic appendages, against the ventral surface of the body, the " elbow " between 

 the ischium and the merus reaching the posterior end of the body. They are 

 altogether out of proportion to the rest of the animal, and give it a weird and 

 grotesque appearance. In sub-adult males these appendages are not so long. PL I, 

 fig. 16, represents those of a male 3*5 mm. long, but while these are of the same 

 general form as in the fully grown male, the ischium and merus are very much shorter 

 and the elbow does not extend much more than half-way along the body. I have 

 no specimens of the first stage in the development of these appendages, from 

 S. Georgia, but two specimens from " Terra Nova " Station 220, which I refer to this 

 species, are immature males in this stage. PL I, fig. 15, illustrates the distal part of 

 their second thoracic limbs. They agree, in general form, with those of the sub- 

 adult male, even to the tooth on the palmar edge of the carpus, but are smaller, 

 the ischium and carpus are not elongated but of normal size, and the whole limb is 

 not any larger than that of the female. Chilton (1909) has described a very similarly 

 marked sexual dimorphism in Munna neo-zelanica, Chilton, which he, therefore, refers 

 to the genus Haliacris, in the light of Miss Eichardson's observations (1906) on 

 H. antarctica, in which she was the first to discover evidences of the marked sexual 

 dimorphism of this species. Miss Richardson's figure of the second thoracic limb of 

 the male of this species, judging from my own observations, is taken from a sub- 

 adult male. It difi"ers from my figure of the same stage in having the merus longer 

 than the ischium, whereas in my specimens of all stages the ischium is longer than 

 the merus. It is possible, therefore, that Miss Richardson had under observation a 

 closely allied Antarctic species, and this has led me to doubt whether all the recent 

 records of H. antarctica from Antarctic waters really refer to this species, or whether, 

 after all, H. australis, Hodgson, is a distinct species, more markedly polar in its 

 range, to which the records of recent writers under the names II. antarctica and 

 H. australis really refer. The matter cannot be cleared up until fully adult males 

 from Antarctic waters are available. 



The discovery of so marked a form of sexual dimorphism in this species naturally 

 raises the question how far such a dimorphism is in reality developed in the genus 

 Munna and its allies, and how many new species of the latter genus have been 

 established on immature specimens. The genera Munna and Haliacris are undoubtedly 

 very closely related. Pfeffer, who had no adult males at his disposal, gave no 

 satisfactory characters for the separation of the genus from Munna; Hodgson, in 

 describing Haliacris australis, suggested that the genus was synonymous with Munna ; 

 and Chilton, in spite of the marked sexual dimorphism of his species Munna neo- 



