Bosmina obtusirostris. 301 



adult. The ocular protuberance is much less marked and the 

 rostrum better developed. 



The shell is plainly striate in the dorsal portion. The mucro 

 is long, directed obliquely downward and in the adult is smooth. 

 In the young some specimens have it smooth and others have 

 two notches on the dorsal side. 



The antenna in the adult is very short, hardly projecting be- 

 yond the beak. The postabdomen shows two or three well- 

 marked rows of small teeth at the infero-posteal angle and a 

 pecten of 6-8 teeth on the caudal claw. The eye is of moderate 

 size and the lenses project but little beyond the pigment. 



The male was not present in the collection. 



Bosmina obtusirostris was first described by Sars ('62, p. 153,) 

 from Norway. It has since been reported from Lapland by Richard 

 ('89, p. 5.), from Siberia (Tobolsk) by De Guerne and Richard. 

 ('91b, p. 234.), and by Poppe and Richard ('90, p. 78.), as possibly 

 occurring in China. Sars ('90, p. 11, 40.), mentions it again 

 from Norway with two varieties, major and alpina. Bosmina 

 brevirostris, P. E. Mueller ('68, p. 97.), has been generally con- 

 sidered identical with B. obtusirostris, but Sars ('90, p. 40.), re- 

 gards the two species as distinct.* Bosmina arctica, Lillj, is a 

 very closely allied species according to De G-uerne and Richard. 



It is of course very difficult to identify species of this genus 

 and I am not confident of the correctness of this identification 

 although it is evident that this species is very close to B. 

 obtusirostris. There is only one description of the species, that 

 given by Sars originally. This account agrees with my speci- 

 mens so far as it goes, but is rather brief, and no figures .of the 

 species have been published. No description mentions the sin- 

 gular form of the ocular protuberance or the unusual position 

 of the teeth of the mucro in the young. 



* Sars quotes the species as B. brevicornisY.~Ei.~M.., but Mueller has 

 no such species in any paper known to me. B. brevicornis was described 

 by Hellich, '70, p. 60. 



