1 882.] and Adjacent Waters. 541 



female the abdomen is usually bent outward to the left, to leave 

 space for a finger-like process which arises at the hind end of the 

 ovisac and curves upward beside the second segment. This is the 

 spermatophore, the neck of which is firmly cemented to the under 

 side of the abdomen. In this sex the legs of the fifth pair are ex- 

 tremely simple and rather small. They are not branched like the 

 other legs, and are without the delicate and beautiful fringes of 

 feathery hairs with which the swimming appendages are provided, 

 but each consists of a single flat, three-jointed plate, with five spread- 

 ing spines at and near its tip. The swimming legs of both male 

 and female are peculiar in the fact that the inner branch of all the 

 pairs is reduced to a single joint. The affinities of this genus are 

 with Heterocope Sars, found in the lakes of Scandinavia, Switzer- 

 land and Upper Italy, and probably in other parts of Europe also; 

 but the modification of the abdomen as a prehensile organ is a 

 new idea among Copepoda. Mutilated specimens of the female 

 of this species have been taken by Mr. Thomas from the water 

 supply of Chicago ; I also found the species common in Geneva 

 lake, in Southern Wisconsin, in October, 1881. 



Another beautiful member of this family, occurring abundantly 

 everywhere in the lake and at all seasons of the year, is closely 

 related to the Diaptomus gracilis of Europe; but a careful study 

 of it during successive seasons, and a comparison with the orig- 

 inal description of Sars and with the descriptions and plates of 

 D. gracilis published by Gruber in 1878, have satisfied me that 

 our species is distinct, and I therefore propose for it the name of 

 Diaptomus siciiis (PI. vin, Figs. 9 and 20). It is the most slender 

 and elegant of our Calanidas, usually colorless and transparent, 

 but sometimes crimson in spring. The antenna? are long and 

 w eak, reaching beyond the tip of the abdomen, and are provided 



reaching beyond the fourteenth. It is in the fifth pair of the legs 

 of both male and female that we find the best distinguishing 

 characters in rhk kmilv—anH h P m thr rarest distinct ions 





acilis occur. In the 



branched. The last joint of the right leg forms a slender, sickle- 

 shaped hook, which is regularly curved from base to apex, while 

 nch of the left leg of this pair is two-jointed, with 



the 



