178 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
about the lower part. The smaller species are frequently deeply col- 
ored with pink, purple and brown fatty deposits and the markings are 
more conspicuous than in the American EHwrycercus, which is itself 
often brightly spotted with blue or purple. The aspect in the water 
is between that of Hurycercus and Daphnia. 
The first mention made of any member of this genus in America is 
Say’s description, repeated in Dekay’s Crustacea of New York, of 
Daphnia angulata. This description which follows is quite sufficient 
to identify the genus, and indeed to indicate that either S. americanus 
or a related form is intended, butit is hardly competent to alter names 
the significance of which is quite clear. 
‘*Sides striate with numerous parallel minute oblique lines; hind 
edge of the body with a prominent angle in the middle. Antenne 
with four filaments on the upper and five on the lower branch. Color 
white or red. Length 0.1mm. Stagnant water in the forests of the 
Southern states.”’ 
*Simocephalus vetulus Mueller. 
PLATES XLIV, Fia. 7; LII, Fias. 6-9. 
‘Daphnia vetula—Baird, Herrick. 
Daphnia sima—Mueller, Latreille, Bosc, Ramdohr,Gruithuisen, Desmarest, Lamarck, 
M. Edwards, Koch, Gmelin, Manuel, Jurine, Lilljeborg, Leydig. 
This commonest and one of the largest species is apparently dis- 
tributed over the northern hemisphere and abounds in all the more 
shallow lakes. The head is rounded in front and is not angled between > 
the prominence of the eye and the beak. The body is very large and 
not abruptly angled above, the spine of the shell being inconspicuous 
and high, so that the free posterior edges of the shell lack little of 
equaling the greatest height of the shell. The shell is covered with 
minute dense striations which spring from the free edges. The pig- 
ment fleck is elongated in old specimens and the upper angle follows 
up beside the suture separating the antennary basin from the rest of 
the shell of the head. The antennules are ornamented with minute 
spines. At the lower angle of the shell are three curved spines which 
differ from the preceding filaments. The number of eggs which are 
produced at once is truly immense. Under favorable circumstances 
this species reaches a large size, falling little if any short of 3.0 mm. 
S. vetulus lives, by preference, among the leaves of aquatic vegetation. 
With us this species seems to live in the smaller pools as well as in 
lakes of some size. JI am not able to see any difference in this respect 
between the various species. 
