1914.] NATURAL SCIENCES OF PHILADELPHIA. 21 



C. bicolor Sars with C. varicans Sars. Many of hor drawings, however, 

 are excellent, and she has furthermore presented all figures on the 

 same scale, which is of value in a comparative study of the species. 

 Her chief source of information has apparently been Herrick, whose 

 work, while remarkable, considering the number of species described, 

 is, owing to its large field, often misleading and at times quite incor- 

 rect. She has neglected both Schmeil and Forbes — the most com- 

 plete modern works on the subject. Her most careful study has 

 been on the armatures of the four pairs of swimming feet, which, 

 while interesting in showing the variations that occur, are not 

 sufficiently constant characters to warrant a deduction of general 

 conclusions. 



E. B. Forbes was the first American investigator to lay much 

 stress on the importance of the shape of the receptacidum seminis. 

 He w^as convinced by Schmeil's work of '92 that it was the most 

 important character for specific distinction. Its shape, while often, 

 somewhat obscure, varies very little, and the same general outline 

 is preserved in all members of the same species. This outline is 

 effected largely by the number of spermatozoa contained in the 

 receptaculum. Other important distinguishing characters are the 

 number of female antennal segments, the length of the first female 

 antennae, hyaline plates and sensory hairs and clubs, armature of 

 the stylets (variable in some species), and the shape and armature 

 of the fifth foot. 



The number of female antennal segments is usually quite constant. 

 Of the specimens from this locality, C. phaleratus and C. varicans 

 were the only exceptions to the rule. The former may have either 

 ten or eleven joints and the latter eleven or twelve. In the plate of 

 C. varicans I have shown only the eleven-jointed form of the first 

 antennae, as this seems to be a winter transitional stage, though such 

 individuals were all sexually mature. The twelve-jointed form did 

 not appear until the April collections. The length of the female 

 first antennae varies remarkably in C. serrulatus, but in all species 

 having antennae of less than twelve segments, it is quite constant. 

 Hyaline plates vary very slightly as to their edges. Minute serra- 

 tions occasionally appear or are absent, notably in C. prasinus. 

 Sense-clubs and hairs are constant features. 



The armature of the stylets and their proportions are constant in 

 some species, as C. modestus, C. varicans, and C. phaleratus. In 

 others, as C bicuspidatus and especially in C. serrulatus, the variation 

 is very great. 



