ENTOMOSTRACA OF MINNESOTA. 3 251 
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 sete. 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 4. exvcisa. Thus this species 
combines the form of abdomen of 4. 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. 
* Alonella excisa Fischer. 
PLATES XXII, Fie. 10; LXI, Fias. 6-7; LXIII, Fias. 10, 11. 
Lynceus excisus—Fischer. 
Pleurovus 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 insculptus). 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, apparently, which has the 
same peculiar markings; and even the common Alona oblonga 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 Pleuwroxus 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 
