238 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
GENUS LYNCEUS. 
Sus-Genus ALONA—Section A, Alona vera. Section B, Alonelia. 
Sus GENus PLEUROXUS—Section A, Pieuroxus verus. Section B, Leptorhynchus.* 
Characters of Percantha and Rhypophilus are combined in the species 
P. procurvus, Birge, so that one must be dropped or new diagnoses 
formulated. JI am not sure that the same species is not at first Pleu- 
roxus verus’ and only later assumes the form known as Rhypophilus. 
So with Percantha the amount of serrature of the posterior margin is 
in part a question of age. 
SUB-GENUS ALONA. 
This group contains two sections which resemble each other in form 
and, in general, in detail; but it is exceedingly difficult to formulate 
a diagnosis that shall strictly limit it. The form is generally sub- 
quadrangular with rounded corners; the terminal claw is armed with 
but a single spine at the base; the beak is rather short; and the pre- 
vailing marking consists of longitudinal lines. 
Section A, Alona (vera) Baird. 
This genus contains a large number of minute animals which are 
widely distributed. 
The authors who have done the most to elucidate this genus are 
Schoedler, P. E. Mueller and Kurz. Birge has contributed most 
largely, thus far, to the knowledge of American species, which are, for 
the most part, identical or very close to the European. No other 
genus is so difficult among the Lynceide, for the most minute differ- 
ences are relied upon to distinguish species. The species of this genus 
are not greatly altered by the production of the winter eggs. The 
males are frequently but little smaller than the opposite sex, and are 
recognized by the altered form of the post-abdomen and the presence 
of a hook on the first foot. The form is more perfectly rectangular 
than in the next section; the shell is only exceptionally reticulated 
and very rarely tuberculate, occasionally smooth. The lower angle 
of the shell is not armed with spines, but is generally rounded. There 
is only one basal spine upon the claw of the post-abdomen, which 
usually bears a row of scales beside the anal spines. The antennze 
have eight sete. The claw of the male post-abdomen is removed from 
the lower angle. 
Many species are known, all of which that seemed recognizably de- 
fined have been included in the following key, which is believed to 
1 Instead of Harporhynchus, a name preoccupied in zoology. 
2 Embryos of P. procurvus have the part which is to be curved forward attenuated before leaving 
the brood cavity, however. 
