ENTOMOSTRACA OF MINNESOTA. 197 



this species are the well crested head, which iu young as well as 

 sometimes older specimens has a median hyaline ridge, the with- 

 drawal of the eye from the margin and the very long spine. It resem- 

 bles I>. galeata in earlier stages. It is very much like D. Icevis or, in 

 other words, is in the group of ]>. Injalina. This form has only been 

 found in autumn, September to November, Lake St. Croix and Eich- 

 field in Hennepin county. 



[*Dapliiiia tliorata Forhes.] 

 Forbes '93. 



"This species belongs to the hyalina group, and may possibly be 

 entitled only to varietal rank. The distinctness and constancy of its 

 characters, however, in collections made by us in Flathead and Swan 

 lakes in western Montana, and the number of minor points in which 

 it differs from hijalina, as most recently described, lead me to distin- 

 guish it as a specific form. 



"It is oval in outline; the long and slender posterior spine is 

 placed at or a trifle above the middle; the length of the head is about 

 a third that of the valves of the shell excluding the spine, and there is 

 no trace of dorsal emargination between head and body. The head is 

 narrowed toward the base and elongated forward in a way to give io 

 the outline of a bell jar with a flaring base. Its front is broadly and 

 regularly rounded, its ventral margin usually conspicuously concave 

 and closely like the dorsal, although occasionally the head is straight 

 or convex beneath. The posterior margin is either straight or slightly 

 concave, and the beak stands free from the front margin of the valves, 

 and by its extension downward not only covers the antennae but 

 reaches clearly beyond the tips of the sensory hairs. The eye is of 

 medium size, placed far back of the front of the head and equidistant 

 from the tip of the beak and the dorsal junction of the head and bod\ . 

 The pigment speck is of moderate size, placed directly behind tlie 

 eye, and much farther from it than from the posterior margin of the 

 head. The antennae are moderately stout, entirely smooth except for 

 inconspicuous transverse rows of minute appressed hairs upon both 

 peduncle and rami, and a row of short, tooth-like spinules at the dis- 

 tal end of each segment. The swimming hairs are rather slender, the 

 second joint commonly decidedly shorter than the first. Fornices 

 slight, arising above and a little behind the eye and terminating 

 directly behind the antennae, above the bases of which they project 

 but slightly. The lower margin of each valve is set with the usual 

 spinules almost to the beak, and the dorsal margin is similarly armed 

 for a distance in front of the spine about equal to half the lepg^ih of 



