IOWA ACADEMY OP SCIENCES. 
165 
head, .46 mm. Ephippial female, length, 1.64 mm.; spine, 
.20 mm.; head, .35 mm.; depth of head, .80 mm.; greatest 
depth of shell, .94 mm.” 
A comparison with the measurements given of D. hybus 
shows the latter to be a much larger form, in some instances 
approaching a length and depth double that of D. minnehaha. 
In the “ Preliminary Notes on the Iowa Entomostraca,” pub- 
lished in the proceedings of the Iowa Academy of Sciences, vol. 
Ill, I followed the classification of Birge and Herrick, and 
placed Daphnia retrocurva, Forbes, in the list as a va^riety of 
Daphnia kalbergiensis, Schoedler. At that time I had not seen 
the original description of either species. 
In Forbes’ description of D. retrocurva first published in the 
American Naturalist, vol. XVI, page 642 , August, 1882 , he says: 
‘ ‘ The shell is reticulate and its spine long and straight, there 
is no macula nigra, and the caudal claws have a row of teeth at 
their base.” The row of teeth referred to is the accessory 
comb. The teeth of the comb are often very small and hard to 
distinguish, but in all the specimens of D retrocurva. I have 
examined they are present. In ‘‘Die Cladoceren des PVischen 
Haffs,” published in 1886 , Schoedler gives his origiD.al descrip- 
tion of D kalbergiensis under the ii ime Hyalodaphnia kalber- 
giensis. The statement in regard to an accessory comb is: 
“Die Schwanzklauen sind ohne secundare Zahnelung.” 
The presence or absence of the accessory comb is recognized 
by sysiematists as a specific character. Hence D. retrocurva 
cannot be ranked as a variety of D. kalbergiensis but as a dis- 
tinct species. In his “Notes on Cladocera Crustacea at Madi- 
son, Wis.,” Birge suggests the propriety of separating the 
American forms from the European D. kalbergiensis, because 
of the pectinated caudal claw, and says: “ Tnis would prob- 
ably bear the name D. keruses, Cox.” 
The note by Cox in the American Monthly Microscopical 
Journal of May, 1883, in which the name of D. keruses is pro- 
posed for this remarkable form is an incomplete description 
and the illustration is not accurate. The description of the 
species with -the proposed name D. retrocurva was published 
in August of the preceding year. 
It is evident that the form described under the names D. 
retrocurva and D. keruses is not a variety of D. kalbergiensis, 
but is species D. retrocurva, Forbes, of which D. keruses, Cox, 
is a synonym. 
