150 TWELFTH ANNUAL REPORT. 



vergentes, reflexa^- segmentum 3-tium corporis fere attingentes. Pedum natatoriorun* 

 structura fereeadein ac in speciebus aiitecedentibus ; aculeorumapicaliuni rami interi- 

 oris pedum 4-ti paris exterior dimidiam fere interioris attingens longitudine. Pedum 

 5-ti paris articulus basalis minimus ultimo multo brevier parumque latior. Sacci ovl- 

 leri mediocres rotundato-ovales abdominique appressi. Lougit. circit. 2 mm. 



(b) Terminal segment of fifth foot with two rather long setae. 

 * External and internal caudal setae not extremely short. 



Sp. 14. Cyclops oithonoicles, Sars. 



(Plate S. Figs. 2—6.) 



f C. hyalinus, rehberg. 

 f U. tenuissimus, hekrick. 



This most interesting species occurs under peculiar circumstances. 

 It is perhaps the rarest member of the genus and seems, beyond a 

 doubt, nocturnal in its habits. It was first found by Sars in saline 

 water and named, on account of its slender form, from the marine 

 Oithona. A similar species which, though about half as large, is 

 hardly distinct, was found by Rehberg near Bremen. Rehberg men- 

 tions particularly that it was found oftener at night than during 

 the day. In America a similar species was described from near 

 Paducah, Ky., under the name C. tenuissimus; but the possibility of 

 identity with the Scandinavian species seemed excluded by the 

 habitat. A gathering taken at night from one of the lakes near 

 Minneapolis contained a few specimens of similar characters, and 

 there no longer seems to be a doubt of the identity or very close 

 relation between these forms. 



The antennas are longer than described for C. tenuissimus, nearly 

 equalling the thorax. The last joint of the antennae is short, but 

 the toothed character was not noted. The fifth feet are small, the 

 spines are very long and slender. The margins of the abdominal 

 segments are irregularly toothed. The species will be confused 

 with no other. It is marked with blue in spots. Length 0. 5 — 1. 

 mm. 



Sp, 15. Cyclops simplex, Poggenpol. 



Cyclops Leeuwenhoeku, hoek (fide Rebberg). 



This species is of more compact form than the last, which it re- 

 sembles in the form of the caudal stylets and the fifth foot. The 

 antennae are nearly as long as the thorax, the last two joints being 

 elongate and having a knife-like ridge which has at the end teeth 

 like those figured in C. tenuissimus. Length 1. — 2. mm. 



