1914.] NATURAL SCIENCES OF PHILADELPHIA. 45 



Subgenus EUCYCLOPS Glaus. 



dyclops prasinus Fischer. PI. HI, figs. 1-5. 



Cyclops prasinus Fischer. '00, pp. ().52-654, pi. XX, figs. 19-26a. 



Cyclops fluriatiliH Ucrnck, 'S2, p. 2ol, pi. VII, figs. 1-9. 



Cyclops magnoctarus Cragin, 'S3, pp. 70, 71, pi. Ill, figs. 14-23. 



Cyclops prasinus Sfhmeil, '92, pp. 150-156, pi. V, figs. 1-5. 



Cyclops fluviatiiis Herrick and Turner, '95, pp. 114, 115, pi. XXVI, figs. 1-8; 



pi. XXX, fig. 1. 

 Cyclops prasinus Forbes, '97, pp. 57-59, pi. XIX, figs. 1 and 2; pi. XX, 



figs. 1 and 2. 

 • Cyclops fluviatiiis Brewer, '98, pp. 135, 136. 

 Cyclops prasinus v. Daday, '06, p. 180. 

 Cyclops fluviatiiis Byrnes, '09, pp. 28, 29, pi. XV, figs. 1 and 2. 



Specific Description. — The form of the cephalothorax in this, the 

 smallest species found in this locality, is that of an ellipse slightl}" 

 flattened at the. ends. The first segment is to the total length of the 

 cephalothorax as 5:7. Its length is to its width as 5:4. The 

 lateral angles of all the thoracic segments are obscure. Their 

 posterior borders are unserrated. The lateral edges of the last 

 segment bear each a fringe of very minute hairs (PI. Ill, fig. 5). 



The abdomen, which is to the cephalothorax as 5 : 9, is rather 

 slender and tapers only slightlj" towards its posterior end. The 

 first segment is enlarged at its anterior end and about as wide as the 

 last cephalothoracic segment. The posterior borders of all the 

 abdominal segments are unevenly and minutely serrated. 



The short stylets (Pi. Ill, figs. 1 and 2) stand well apart in the 

 living animal. The lateral spines are situated f of the length of the 

 stylets from their anterior end. Of the apical setse only two are 

 well developed. The inner and outer bristles are small. Of these 

 the outer is much heavier and is slightly shorter than the inner. 

 Neither attains the length of the stylets. Of the large middle pair 

 the inner is to the outer as 5:3. Brewer gives 4 :5 "or equal." 

 The larger of the two is four times, the shorter about three times, as 

 long as the stylets. Both are delicately plumose. 



The first pair of (twelve-jointed) antennae (PI. Ill, fig. 1) reach in 

 the female to the posterior border of the third thoracic segment. 

 Forbes finds them often reaching "quite to the first abdominal 

 segment. " The eighth joint is the longest, exceeding that of the two 

 preceding segments. Dr. Schmeil finds on the ninth segment a 

 "well-developed sense-club," and, in his foot-note, states that 

 Richard "even denied the presence of a sense-club." All of my 

 specimens agree with Forbes' description in the absence of the 

 sense-club, but "minute sensory bristle" on the tenth segment. 

 This seems, then, to be undoubtedly a characteristic point of differ- 



