STATE GEOLOGIST. 153 



has much shorter stylets and differently proportioned antennae, etc. 



Length 1.5 ram. Thorax 0.9 mm.; abdomen 0.6 mm.; stylets 

 <0.14 mm,; last two abdominal segments 0.16 mm.; antennae 0.7 mm.; 

 first segment of body 0.5 mm. The basal segment of the antennae 

 is long and ornamented with several transverse series of spines, the 

 last two segments are equal and longer than tlie preceding. The 

 armature of the first and fourth feet is identical with C. thoma-i, as is 

 the form of the female openings and the fifth feet. The form of 

 the first feet, candal stylets and other details were correctly figured 

 on plate V of the Cyclopidae of Minnesota. 



Specimens of Cyclops piilchellas (thomasi) were obtained from a 

 •cistern which is supplied solely by rain-water. The eggs must have 

 been introduced in ice which had been placed in the cistern at least 

 a year previously. The cistern is entirely dark, so that these ani- 

 mals must have been deprived of light for many generations. The 

 general color was of course very white; the eye spots were pale, but 

 present with some pigment and the lenses. No noticeable altera- 

 iion in form had resulted. 



(c) Terminal segment of fifth foot with three setae. 

 Sp. 17. Cycloijs teniiicornis, Claus. 



(Plate R. Fig. 16.) 

 ■var. a. Knife-like ridge upon tlie antennae smooth. 



L. albidllS, JUKINE, 



C. quadricornis, var. h, baird. 



C. tenuicornis, saks .lubbock, heller, fric,uljanin, hoek, brady, herrick. 

 C claii^ii, roGGENPOL. 

 C. annulicorais, sars. 

 var. b. Knife-like ridge of antenna; toothed. 

 C. obesicornis, templeton. 

 C. sigfiatus, koch, sars, ul.ianin, krady. 

 C. coronatus, claus, i.ubbock, heller, fric, hoek. 

 C. signatus, var. fasciacornis, cragin. 



Cyclops tenuicornis, as thus comprehended, is widely distributed 

 and variable. European specimens in our collection have longer 

 stylets, but seem otherwise identical. The nearest relation is C. 

 ater, which is easily distinguished by the compact oval form of the 

 thorax and the one-jointed fifth foot. In the stage previous to 

 maturity the ''signatus" form has no teeth upon the ridge of the 

 last segment of the antennae; it is then similar to the C. tenuicornis. 



Cephalothorax broad; abdomen rather slender; antennae reaching 

 -about to base of thorax, attenuated at the end; terminal joint with 



a knife-like ridge; formula— -^ — r---^---ww^ ; fifth 



foot composed of a long basal joint bearing a long spine and a ter- 



