SYSTEMATIC REPORT 169 



to the apex of the endopod in M. australe and their arrangement into weak series is quite distinctive 

 and cannot be attributed to the immaturity of the specimens. In other species of mysids, it is found 

 that, when spines are arranged in series of larger spines with smaller ones in the spaces between them, 

 the condition tends to become more pronounced with age. The telson in M. mixta is relatively shorter 

 and broader than in M. australe and the spines arming the lateral margins are larger and more regular 

 in size and spacing. 



This is the first species of the genus to be described from the waters of the southern hemisphere. 

 Unfortunately there are no male specimens available and until the male pleopods are seen it is not 

 possible to say whether the secondary sexual modification in the fourth pair is the same as that shown 

 in other species of the genus. 



Distribution. The present specimens were taken at two stations to the west of South Georgia in 

 vertical hauls of 50-0 m. 



Genus Neomysis Czerniavsky, 1882 



18826 Heteromysis Czerniavsky, 2, p. 33. 



1882-36, c Neomysis Czerniavsky, 2, p. 23; 3, p. 81. 



Remarks. In his revision of the tribe Mysini, Zimmer (1915a, p. 214) amalgamated the genera 

 Neomysis Czerniavsky and Acanthomysis Czerniavsky, as he considered that the only difference be- 

 tween them, the acutely pointed, unsegmented antennal scale in Neomysis and the two-segmented 

 scale with rounded apex in Acanthomysis, was not of sufficient generic significance to warrant the 

 existence of both genera. Tattersall (1932, p. 317) suggested that since a considerable number of 

 species had been referred to the two genera, it might be convenient to retain them both, as the 

 shape of the antennal scale forms an easy means of dividing them into two groups. Ii (1936, p. 579) 

 agreed with this suggestion and restored the genus Acanthomysis. 



Tattersall (195 1, p. 180) drew attention to the fact that, in all the species of Neomysis which he had 

 examined, with the exception of N. spinosa Nakazawa, breeding females possessed a median finger- 

 like sternal process on each of the last two or three thoracic somites. He had not examined specimens 

 of N. monticellii Colosi, N. patagona Zimmer and N. meridionalis Colosi and he thought that, if these 

 species were found to possess sternal processes also, their presence might form a useful generic 

 character, since no such processes have been recorded from any species of Acanthomysis. Unfortu- 

 nately there are no female specimens of Neomysis monticellii in the Discovery collection and I am 

 unable to ascertain whether there are sternal processes in the females of this species, but in the 

 abundant captures of N. patagona I have been able to examine females in all stages of development. 

 In no case could I find any sternal processes in this species. 



The marsupium is composed of two pairs of brood lamellae, which are borne on the last two pairs 

 of thoracic appendages in females. In addition there is, in most species of the genus, a rudimentary 

 brood lamella in the form of a small knob, armed with a group of extremely long non-plumose setae 

 on the bases of the sixth abdominal appendages. Similar rudimentary oostegites have been recorded 

 in some species of Acanthomysis and it is probable that they occur in other species of both genera but 

 have not been noticed. 



Neomysis patagona Zimmer, 1907 

 (Fig. 42 A-K) 



1907 Neomysis patagona Zimmer, pp. 1-5, figs. 1-17. 



19 1 3 Neomysis patagona, Hansen, p. 21, figs. 



1921 Neomysis patagona, Hansen, p. 5. 



1 95 1 Neomysis patagona, W. M. Tattersall, p. 180. 



