114 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



* Cyclops fluviatilis Herrick. 



Plates XXVI, Figs. 1-8; XXX, Fig. 1. 



Herrick '82, '84 and '87; Cragin '83 (magnoctavus); Brady '91 (niagnoctavus); 

 Turner '92; Marsh '93. 



This small species, first described iu America, has been encoun- 

 tered by Brady in Great Britain, though he chooses to make the com- 

 parison to CalanidiB 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 larger and particularly the highly colored 

 condition is conspicuous especially by reason of its rapid motions. In 

 appearance it reminds one of Gyclopsina 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 autennie are nearly as long as the whole 

 thorax, and are remarkable for the elongation of the seventh to ninth 

 segments. There are elongated setse upon the first and fourth segments. 

 The last joint of the antennte 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 maxillfe have the usual form. The feet are peculiar in the 

 exceedingly long setai. The armature of the apical segments is as 

 follows: 



First Foot. 



(ex. 3 spines. f ex. 1 seta, 



ap. 2 setae. Inner ramus i ap. 2 setje. 



in. 3 setse. (.in. 3 sefse. 



Second akd Third Feet. 



!ex. 3 spines. f ex. 1 seta, 



ap. 1 spine, 1 seta. Inner ramus i ap. 2 seffe. 



in. 4 setse. (in. 3 sette. 



Fourth Foot. 



{ex. 2 spines. Tex. 1 seta, 



ap. 1 spine, 1 seta. Inner ramus < ap. 1 spine, 1 seta, 



in. 4 setaj. (.in. 2 setse. 



The fifth foot is small, one-jointed, and bears three small set£e. The 

 abdomen is slender, though rather short. The stylets are three times 

 as long as broad. The outer of the terminal setse 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 



