396 Wisconsin Academy of Sciences, Arts, and Letters. 



this fonn. The relationship of this group, then, may be ex* 

 pressed by the following diagram : 



Bicilis 

 Birgei 



Ashlandi 



tenuicaudatus 



minutus 



D. Tyrelli has no appendage of the antepenultimate segment 

 of the right male antenna, but the structure of the male fifth 

 foot leads me to think that it should be classed with this group. 

 It must be considered as somewhat distinctly separated from 

 the rest of the group, and its phylogeny is uncertain. 



THE LEPTOPUS GROUP. 



This includes D. leptopiis, leptopus var. piscinae, corvipe- 

 datus, stagnalis, Lintori^l, spatulocrenatus and clavipes. . . D, 

 compedatuSj, D. spatulocrenatus and D. stagnalis have a hook 

 on the antepenultimate segment of the right antenna of the 

 male. The others have a lateral hyaliLe lamella. D. lepto- 

 pus, D. leptopus var. piscinae, D. conipedatiis and D. clavipes 

 have a hook in the posterior face of the second basal segment 

 of the right fifth foot of the male, this hook being most pro- 

 nounced in the case of D. clavipes. The published figures do 

 not indicate the presence of such a hook in D. Lintoni or D. 

 stagnalis, but Schacht's description of D. stagrmlis speaks of 

 the presence of a "large, smooth, hyaline lamella." This may 

 represent tlie hook of the other species. In the female fifth 

 foot, the second segment of the exopodite has either two or 

 three spines in D. leptopus, and three in D. clavipes, D. conipe- 

 datus, D. spatulocrenatus and D. Lintoni. In D. stagnalis the 

 exopoclite is distinctly three-segmented. The endopodites of 

 the female fifth feet in D. stagnalis are two-segmented. 



