STATE GEOLOGIST. 159 



tinteriorly ; last segment fringed at the angles with numerous fine 

 hairs. Antennae much shorter than in C. serrulatus, about as long 

 as the first thoracic segment, otherwise similar. Abdomen attenu- 

 ated, penultimate segment margined posteriorly with spine-like 

 setse, the other segments pectinated. Caudal stylets very long and 

 slender, about equal in length to the three segments preceding, 

 bearing a group of four to five spines on the outside near the end, 

 otherwise unarmed. Length 1.3 mm. 



Here is the natural place for C. spinulosus, of Glaus, but there is 

 strong reason to suspect the validity of the species so very imper- 

 fectly characterized. 



Sp. 26. Cyclops fluviatilis, Herrick. 



(Plate Q5. Figs. 1—9.) 

 Cyclops magnoctavus, cragin. 



This small species with twelve-jointed antennae and conspicuous 

 ■coloration is widely distributed through the Mississippi valley. The 

 original description is appended. 



''Body elongated; thorax very long; abdomen slender; stylets 

 about as long or longer than last abdominal segment; setae all very 

 short, not [always] pectinate; lateral and dorsal setae very small; 

 outer one spine-like, short and stout; two median setae short; inner 

 one very small and inconspicuous; antennae reaching nearly to the 



base of abdomen [or beyond]; formula— — ^ — - ; the 



three joints following the six basal are much elongated, while the 

 terminal ones are but moderately so, a character which is peculiar 

 to this species; terminal segment slightly but evidently hinged and, 

 together with pair preceding, somewhat curved; feet with the ter- 

 minal spines strongly toothed; fifth foot very small, one-jointed, 

 bearing three small setae; operculum vulvae heart-shaped; egg-sacs 

 sub-quadrangular; eggs large; abdomen in the young much 

 elongated. Color deep indigo. Length 0.7 mm." 



The first foot has upon the last joint of outer ramus three ex- 

 ternal spines, two apical setae and three internal setae; the outer 

 branch of fourth foot has three external spines, apically a spine and 

 seta and internally four setae. 



Males of this species are slender, measuring about 0.75 mm.; the 

 abdomen being 0.28 mm., stylets 0.6 mm., first thoracic segment 

 0.28 mm., and the longest caudal seta 0.24 mm. The antennae are 

 long and much modified so as to resemble superficially the antennae 

 of Diaptomus. 



