1878. 



C 



1882. 



u 



1883. 



it 



1883. 



it 



1884. 



a 



1885. 



a 



1886. 



a 



1888. 



a 



1890. 



a 



1890. 



a 



1891. 



a 



1891. 



u 



1891. 



a 



1892. 



a 



1893. 



a 



18 MICHIGAN FISH COMMISSION— BULLETIN NO. 5. 



C. tenuicornis Brady, p. 102, pi. XVII, figs. 1-10. 

 " Herrick. 



Cragin, p. 3, pi. II, figs. 1-14. 

 signatus var. fasciacornis Cragin, p. 2, pi. II, fig. 15. 

 tenuicornis var. a Herrick, p. 153, pi. Q 4 , figs. 1-7. 



Daday, p. 211. 



Vosseler, p. 189, pi. IY, figs. 6-10. 

 albidus Sostaric, pi. I, figs. 3, 4 and 12. 

 tenuicornis Thallwitz, p. 79. 



Lande, p. 36, pi. XVI, figs. 22-32. 

 gyrinus Forbes, p. 707, pi. II, fig. 9; pi. Ill, fig. 14. 

 albidus Schmeil, p. 23. 



annulicornis and tenuicornis Richard, pp. 224-226. 

 albidus Schmeil, p. 128, pi. I, figs. 8-14b; pi. IV, fig. 2. 

 signatus Marsh, p. 211, pi. V, figs. 7-9. 



Schmeil states that the antennae of C. albidus are armed with crowns of 

 spines as in the case of C. fuscus. This seems to be rarely true in our 

 forms. Although I have examined with great care large numbers of mature 

 females, it is only in very few specimens that I have found this peculiar 

 armature. The membrane of the terminal antennal segment is ordinarily 

 serrate. The common form corresponds to the annulicornis of Sars and 

 Richard, which, according to Schmeil, Richard now allows to be a variety 

 of albidus. The distinguishing characteristic of annulicornis is the rudi- 

 mentary seta of the inner margin of the terminal segment of the endopo- 

 dite of the fourth foot. This is represented in most of my specimens only 

 by a minute spine. ( PL VI, fig. 9. ) In two individuals I have found in 

 place of this minute spine a short seta. (PL VI, fig. 8.) In these two speci- 

 mens the circlets of spines were present on the 8th, 9th, 10th, 12th, 13th, 

 and 14th segments. It was this form evidently that Cragin called C. 

 tenuicornis ('83 pi. II, figs. 1-14), as is shown very clearly by the figures 

 of the fourth foot and antennule, although he did not figure the circlets 

 of spines on the antennal segments. (7. signatus var. fasciacornis Cragin, 

 it is not possible to identify with certainty, although it seems probable 

 that it is albidus. C. gyrinus Porbes does not have the antennal circlets of 

 spines, but does have a short seta instead of a minute spine on the fourth 

 foot, thus agreeing with Cragin's figures of C. tenuicornis. This would 

 seem to be intermediate between the two forms I have seen. It is difficult 

 in such a case to tell just where the limits of species should be drawn, for 

 we are entirely ignorant of the life histories of the forms, and it is certain 

 that the Cyclopidce have wide limits of variation. It seems to me safer, 

 for the present, at least, to consider such minute differences as varietal, and 

 not to increase the number of species. 



C. albidus is not very abundant, but occurred in many of the St. Clair 

 collections, and in some of those from other points in Michigan. It is a 

 universally distributed species, but does not occur in great numbers. 



Cyclops pi.uviatil.is Herrick. 



1882. C. fluviatilis Herrick, p. 231, pi. VII, figs. 1-9. 



1883. " magnoctavus Cragin, p. 5, pi. II, figs 14-23. 



1884. " fluviatilis Herrick, p. 159, pi. Q 5 , figs. 1-9. 

 1887. " " Herrick, p. 15. 



