A REVIEW OF THE MYSIDACEA 



59 



inermis it is very short. I suggest that this difference is sexual. The 

 type of B. rostrata is a female and that of B. inermis a male. In the 

 present collection are specimens of both sexes and the male specimens, 

 especially the older ones, agree with Hansen's figures of B. inermis. 

 The female specimens have a longer rostral process than the male 

 though in no case is it as long as shown by Illig. Incidentally the 

 rostral plate is relatively longer in young specimens than in adults 

 (figs. 11, <z, b ; 13) and appears to undergo progressive reduction with 

 growth. The two species are otherwise in the closest agreement, 



Figure 13. — Boreomysis rostrata Illig ? : Anterior end of young specimen to show the rostral 

 plate, eye, antennular peduncle, and antennal scale and peduncle. 



especially in the form and armature of the telson, the very short un- 

 armed portion of the outer margin of the outer uropod (fig. 12, d), 

 and in the shape and proportions of the antennal scale (fig. 12, a). 

 The question of the identity of the two species is rendered more diffi- 

 cult by the fact that Illig's specimens of B. rostrata would appear to 

 include more than one species. The male specimen figured by Illig 

 (1930, figs. 28-35) appears to me to belong to a different species from 

 those representing the female (Illig, 1930, figs. 22-27). No type 

 specimen is indicated and for the purposes of this paper I have re- 

 garded the specimens figured by Illig in figures 22 to 27 as the types. 

 I am convinced that my specimens can be referred to B. inermis Han- 

 sen, and I would record them under that name were it not for the fact 

 that as stated above the specific name inermis is preoccupied within 

 the genus. I think it is very probable that some, at least, of the speci- 



