114 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. | 
* Cyclops fluviatilis Herrick. 
PLATES XXYVI, Fies. 1-8; XXX, Fie. 1. 
Herrick ’82, ’84 and ’87; Cragin ’83 (magnoctavus); Brady ’91 (magnoctavus); 
Turner ’92; Marsh ’93. 
This small species, first described in America, has been encoun- 
tered by Brady in Great Britain, though he chooses to make the com- 
parison to Calanide of the original description a reason for adopting 
a subsequent name. It is one of the most abundant forms in many of 
our lakes and their outlets. In its smaller age form it is barely visi- 
ble to the eye, while the Jarger and particularly the highly colored 
condition is conspicuous especially by reason of its rapid motions. In 
appearance it reminds one of Cyclopsina gracilis. 
The body is slender, the cephalothorax being elongate, oval, with 
its first segment very long. In a specimen measuring 0.57 mm. to the 
end of the stylets, the following proportions were noted: First seg- 
ment of thorax 0.22 mm., second and third segments each 0.056, fourth 
0.032, total length of abdomen 0.17, stylets 0.032, longest seta 0.128, 
outer median 0.10 mm. The antenne are nearly as long as the whole 
thorax, and are remarkable for the elongation of the seventh to ninth 
segments. There are elongated set upon the first and fourth segments. 
The last joint of the antenne is slightly curved and carried at an 
angle to its predecessor during life, giving it the appearance of being 
hinged. It has also the rudiment of a knife ridge. The antennules 
are slender and elongate. The labrum has about twelve small teeth. 
The maxille have the usual form. The teet are peculiar in the 
exceedingly long sete. The armature of the apical segments is as 
follows: 
First Foor. 
ex. 3 spines. ex. 1 seta. 
Outer ramus jap. 2 sete. Inner ramus jap. 2 sete. 
in. 3 sete. in. 3 setz. 
SECOND AND THIRD FEET. 
ex. 3 spines. ex. 1 seta. 
Outer ramus ; ap. 1 spine, 1 seta. Inner ramus jap. 2 sete. 
in. 4 sete. in. 3 setx. 
FOURTH Foor. 
ex. 2 spines. ex. 1 seta. 
Outer ramus ; ap. 1 spine, 1 seta. Inner ramus + ap. 1 spine, 1 seta. 
in. 4 sete. in. 2 sete. 
The fifth foot is small, one-jointed, and bears three small sete. The 
abdomen is slender, though rather short. The stylets are three times 
as long as broad. The outer of the terminal sete is a short spine, 
Shorter than the stylet. The egg-sacs are appressed and contain four 
or five ova in the first state and a few more in the adult. The two 
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