STATE GEOLOGIST. 97 



? Sp. 6. Alona niodesta. (Sp. n.) 



(Plate H, Fig. 3; and Plate Q, Fig. 4.) 



The length varies between 0.41 mm. and 0.55 mm. The smaller 

 forms have the back most rounded, while a specimen 0.55 mm. 

 long will appear very like A. quadrangularis. Males are elongate; 

 hook of first foot strong, accompanied by a heavy growth of small 

 spines; terminal claw of abdomen with a minute spine. 



? Sp. 7. AloDa costata, Sars. 



Founded practically upon the absence of the eighth seta of the 

 antennae. The description given by Sars will not render it recog- 

 nizable so that there is no occasion to repeat it here. In all the 

 species of this section the eighth seta is small and may be absent. 



Sp. 8. Alona quadrangularis, Mueller. 



(Plate E. Figs. 1—2.) 

 Alona sulcata, schoedler. 



Alona quadrangularis, p. e. mueller, ktjrz, herrick. The further synonomy of 

 the species may well be doubtful, for there are species so 

 closely allied as to render a strict determination difficult. 

 Lynceus quadrangularis, o. f. mueller, is the name employed, and is thought to he 

 identical with the Alona quadrangularis of Baird. 



Shell quadrangular, highest behind; lower margin straight; 

 posterior margin curved; lower angle rounded, striped with rather 

 evident lines which are parallel and straight. The beak is quite 

 long; the pigment fleck is smaller than the eye. The post-abdomen 

 is broadest near the end, where it is strongly rounded; the numer- 

 ous anal spines are strong and emarginated, supported by a lateral 

 series of scales; the terminal claw and its basal spine (in American 

 forms) are denticulate (Kurz says smooth in European specimens). 

 The feet are of the typical Alona form (see plate E, fig. 1). The 

 shell gland is rather conspicuous; no true ephippium. The abdo- 

 men of the male lacks the spines, but is otherwise similar. Length 

 0.6 mm. to 0.7 mm. Less abundant in Minnesota than the next. 

 Both this and the following species were recognized in 1878, but 

 were thought to be the same species. (See Microscopic Entomostra^ 

 ca^ p. 109.) 



Sp. 9. Alona oblonga, P. E. Mueller. 



Alona oblonga, KCRZ, BIRGE. 

 Alona quadrangularis, LILLJEBORG. 



Differs from A. quadrangularis in the following points: — the 

 greatest bight of the shell is anterior to the middle; the lines are 

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