66 TWELFTH ANNUAL REPORT. 



5. Eosmina striata , Derrick . 

 tt Antennnles short. 



* Rostium long. 



6. liosmina lacmtris, Sars. 

 ** Rostrum short. 



7. Bosmina obtvsi7-ostrw, SaTB. (B. nitida, Sare?) 



B. Shell not spiued behind. 



(a) Shell strongly arched above. 



8. BosminalilJJ6borgii,Sars, (B. diaphana?) 



(b) Shell moderately curved above. 



9. Bosmina microps, P. E. Mueller. 



Coucerninsj the identification of Bosmina longispina, Leydig, 

 with B. brevirostris, P. E. Mueller, it must be said that the bow is 

 drawn at a venture, for Mueller, in his paper on the Cladocera of 

 Swiss Lakes, in a fit of absent-mindedness refers to B. lacustris, P. 

 E. Mueller, citing p. 149 of Danmark's Cladocera. On ttie page in 

 question are descriptions of B. maritima and B. brevirostris of which 

 the latter is probably the one meant. Sars' B. lacustris seems quite 

 difiierent, being strongly marked by longitudinal lines, while Leydig 

 says of B, longispina "shell striped and small reticulate," and P. E. 

 Mueller says in B. brevirostris the shell is "utydeligt reticuleret" 

 i. e. indistinctly reticulate. 



The three species so far identified in America are B. longirostris, 

 of which a figure is given (plate J, fig. 2,) B. cornuta and B. striata, 

 which may possibly be yet identified with one of the European spe- 

 cies, though it seems improbable. I have also seen a species like 

 L?ydig's B. lasvis, but considered it a smooth variety of B, longi- 

 rostris. 



FAMILY LYNCODAPHNID^, Sars, 1861; Herrick, 1881. 



This is a rather small family with seven genera of minute ani- 

 mals Avhich are abundant only in summer. Many and, indeed, 

 most oi the species are among the rarer of fresh-water crustaceans 

 of this group, and a few are among the rarities which only now and 

 then reward the collector. This family undoubtedly is the link 

 connecting the Daphnidse with the Lynceidse, relationships to which 

 are expressed by Macrothrix, on the one hand, and Lyncodaphnia, 

 on the other. 



The rank of this group as a family must be, of course, a matter 

 largely of opinion. Sars was the first to adopt this view, sustained 

 by certain curious transition forms leading toward Ljmceidie. Later 

 writers seem never to have found these genera and the group was 



