STATE GEOLOGIST. 227 



Grenus cyclofs. 



Brady well says of this genus : "As regards discrimination of species 

 it is, perhaps, the most difficult and puzzling of all the Copepoda. ' ' 

 He also states that " the only safe rule in this state of things is to ac- 

 cept no specimens as types which do not show amongst them ova- 

 bearing females." It is necessary, however, to limit the matter more 

 closely, as will be shown farther on, for not only do immature females 

 become fruitful even while the antennae are yet incompletely developed, 

 but the species are subject to a sort of dimorphism which it is interest- 

 ing to parallelize with that in the males of Cambarus. The species are 

 all fresh-water, so far as it is at present known, though it may be that 

 salt-water forms exist under other names. 



The characters of the family with some limitations apply to the 

 genus. 



The following species are probably but few of those which occur 

 even in Minnesota, but they are so clearly defined, for the most part, as 

 to be unmistakable and their description it is hoped will form a founda- 

 tion upon which to lay later study. — Observations extend over a term 

 of about four years. 



Species with seventeen-jalnted Antennce. 



CYCLOPS TEJ^UICOKNIS, ClaUS. 



Bibliography. 



Plate VI, figs. 1-11, 20. Plate Y, fig. 14. 



Cyclops tenuicornis, Glaus, Das Genus Cyclops. 



Die Frei-lebenden Copepoden^ 

 Sars, Oversigt af de Indenlandske. 



Ferskvands Copepoder. 

 Uljanin, Reise in Turkestan. 

 Brady, British Copepoda. 

 Cyclops signatus, Koch, Deutschlands Crust. 



'(r. 0. Sars. Uljanin. Brady. 

 Cyclops coronatus, Claus. Fric. 



We feel confident that the two forms distinguished by Claus as C 

 coro)iatus^(=^signatus) and C, tenuicornis should be united, as the only 

 distinction which is at all reliable, is the knife-like serratedj^ ridge on 

 the last joint of the antennae. The last joints are frequently longer in 

 tenuicornis form, as are the stylets in eoronatus, but this varies. In the 



