280 Wisconsin Academy of Sciences, Arts , and Letters. 
Schwimmfiisse absolut werthlos sei, es schoint vielmehr, als 
ob die Bedornungsverhaltnisse der Spitze des Innenastes wor- 
auf S'ars und Richard so grossen Wert legen, noch nicbt genii- 
gend beriicksichtigt waren. Die Anzahl der Dornen ist aber 
sicber grossen Sehwankungen unterworfen, und die Angabe 
derselben bat nur einen sebr beschranken Wert.” Forbes, in 
bis paper of ? 97, says.: “The number of antennal segments 
may be depended upon as fairly constant. * * The length 
of the antennae, while constant in some species, is remarkably 
variable in others, notably C. sefrulatus. * * Sensory 
structures and the hyaline plates of the distal antennal segments 
are reliable characters. In certain species, C. plialeratus for 
instance, the proportions of the stylets are quite constant, but 
in C. viridis, serrulatus, and bicuspidatus, the range of varia¬ 
tion is very great; consequently such measurements are not of 
the highest specific value. The apical bristles of the stylets 
are not very variable as to comparative lengths, but the minute 
details of their structure are not constant. This fact is illus¬ 
trated by the variation in the shape of the outer apical spine of 
C. viridis var. brevispinosus. (PI. XI, Fig, 1.) The 
armature of the swimming feet is of considerable value in cer¬ 
tain cases, and is. constant as a rule. Sometimes, however, the 
presence or absence of a spine or seta is not accompanied by 
other perceptible differences. The general character of the 
armature 1 with regard to- strength, etc., may usually be relied 
upon; but I have often seen in a. single specimen all the grada¬ 
tions between spines and setae, and it would be impossible from 
this character to' say which of the two names should be applied. 
Of the easily observable structures, the fifth foot is the most 
valuable for distinction. * * Of all the specific characters, 
the most valuable are those derivable from the receptaculum 
seminis.” I quote also 1 the specific descriptions of C. brevispi¬ 
nosus , given by Herrick, ? 84, and Marsh, ? 92, and that of C. 
americamis , by Marsh, ? 92. Herrick describes brevispinosus 
as follows: “Sp. 10. C. brevispinosus Sp. nov . (PI. S, 
Figs 7-11.) The form for which this name is proposed takes 
the place of the above C. parcus Herrick in the larger lakes. 
