ENTOMOSTRACA. OF MINNESOTA. 251 



moderate size, but smaller than the eye. The post abdomen is short, 

 rounded below, and armed with sharp and small anal teeth, besides 

 which is an inconspicuous row of minute setse. The claw is very 

 small, and has a single very minute tooth. The shell is marked by 

 reticulations, which below are regular hexagons but above pass into 

 elongated meshes, and finally on the beak and head become longitud- 

 inal striations. The areas are lined as in A. excisa. Thus this species 

 combines the form of abdomen of A. exigua with the teeth of Grapto- 

 leberis and the markings of A. excisa. 



Length hardly 0.27 mm. Motion active. The specimen figured 

 contained a single large ovum. The head may possibly have been 

 somewhat protruded by pressure. Habitat, vicinity of Minneapolis, 



*Aloiiella excisa Fischer. 



Plates XXII, Fig. 10; LXI, Figs. 6-7; LXIII, Figs. 10, 11. 



Lynceus excisus — Fischer. 

 Pleuroxus excisus — Schoedler. 

 ? Pleuroxus insculptus — Birge. 



This species is closely allied to Alonella exigua; yet that species 

 shows appreciable differences (which can hardly be claimed, per- 

 haps, for Pleuroxus inscidpius). The various authors who have written 

 of this Lynceid have all laid emphasis upon the sculpture of the shell, 

 almost to the exclusion of other points in the description. Professor 

 Birge has found a quite different form, ajiparently, which has the 

 same peculiar markings; and even the common Alona ohlonga has a 

 part of the valves covered by minute striations. Schoedler's figure of 

 this species is unrecognizable; but, as identified by Kurz, the species 

 seems undoubtedly the same that is common in shallow pools in Min- 

 nesota, during autumn, and probably also in Massachusetts. 



The variations to which this species is subject are considerable and 

 may account for the marked disagreement in the accounts of our dif- 

 ferent authors. Schoedler gives his specimens a length of 0.20 to 0.25 

 mm., while Kurz says 0.35 mm. Birge gives 0.27 mm. for the length 

 of Pleuroxus insculptus. and our specimens varied in the same gathering 

 between 0.24 mm. and 0.40 mm. Schoedler figures three teeth at the 

 lower posterior angle; Kurz says "several (4)"; Birge describes one 

 or two, and Minnesota specimens show gradual transitions from an in- 

 conspicuous angle to three or perhaps four teeth. These teeth are 

 the extensions of some of the strong ridges or crenulations which 

 mark the shell. P. E. Mueller's figures of the shell and abdomen of 

 P. exigua would apply to our species perfectly, save the absence of 

 minute striations; Kurz's statements with reference to the differences 

 between these two forms seem to agree only in part with those of 



