Pe ee ee 
ENTOMOSTRACA OF MINNESOTA. 253 
species from the above seems to be the position and form of the head, 
which is said to be blunt and nearly horizontal, as in Camptocercus 
rectirostris. Is this a transition to Graptoleberis ? 
* Alonella pygmzea Sars. 
PLATE LX, F14. 7. 
Pleuroxus transversus—Schoedler. 
Alonu transversa—P. E. Mueller. 
Lynceus nanus—F rie. 
Alonella pygmxa—Kurz. 
The form is rotund, much like species of Chydorus in the highly 
arched dorsal outline; the beak is rather short and depressed; the 
lower outline of the valves is very convex in front, and barely sinuate 
behind, where it terminates in a minute spine. The shell is marked, 
as in no other Lynceid, by lines running diagonally backward, and 
only on the lower part reticulated, if at all. 
The post-abdomen is short, broad and rounded below; the claw has 
a single basal spine. Length 0.20 to 0.28 mm. This is the smallest 
member of the Cladocera. In form it so nearly resembles Chydorus 
that upon first sight the writer took it for a member of that genus. 
Our one specimen measured 0.25 mm. The shell is marked by plica- 
tions rather than strize, which arch over the back. 
Alonella striata Schoedler. 
This species is said to resemble 4. exigua in habit and sculpture 
of shell; the form is quadrangular and not greatly elevated in the 
middle; the lower margin is nearly straight and fringed with bristles; 
the posterior angle is rounded and unarmed. The antennules with 
their sete extend beyond the beak; the pigment fleck is smaller than 
the eye and half way tothe beak. The post-abdomen is long and nar- 
rowed toward the end; there are seven or eight anal spines, and two 
spines on the terminal claw. Length about 0.5 mm. 
SUB-GENUS PLEUROXUS. 
Section A, Pleuroxus (verus) Baird. 
This group of Lynceids is most obviously defined by the long beak, 
formed by the extension of the chitinous covering of the head. (There 
is rarely a beak in the sense of that word as applied in the ease of 
Scapholeberis or Daphnia, but the antennules are simply attached to 
low prominences on the under side of a broad shield-like projection 
of the shell.) This beak-like projection is acute and often long and 
either curved backward or even bent forward. The fornices, or lateral 
E 
~~ eo 
