196 ESTHER F. BYRNES. 



mentary fifth foot to be the most characteristic organ by which 

 the species can be easily identified even in very early stages. 

 Whether the hairs on the fifth foot are setose or spiny depends 

 in large measure on the age of the individual, and is of little 

 importance. 



There are two generally recognized varieties of the species C. 

 signatus, namely, var. coroiiatits (C. fuscus of Jurine) and var. 

 tenuicornis or annulicornis, called C. albidus by Professor Marsh. 



Both of these forms occur side by side and are regarded by 

 some authors, Herrick and Brady, as transitional stages of one 

 and the same form, while other authors regard them as distinct 

 varieties. 



I do not wish at this time to express an opinion on the rela- 

 tionship of C. coronatns and C. tenuicornis, but the correlations 

 indicated in this paper for C. signatus, var. coroualus, can also be 

 observed in the forms described as C. signatns, var. tcmiiconiis, 

 in which the hairs on the inner margins of the stylets are lacking, 

 as well as the serrations in the hyaline plate in the sixteenth and 

 seventeenth antennal segments ; and in which the second segment 

 of the antennule, as well as the basal segment of the rudimentary 

 fifth foot, are relatively long, while in coronatns they are conspic- 

 uously short. 



The armature of the fourth pair of swimming feet, often shown 

 in keys to the Cyclops, is by itself of little value as a means of 

 identification, since several distinct species agree in the armature 

 of this appendage, although they have no agreement in any of the 

 other swimming feet, nor in the larger outlines of the body. It 

 is to be regretted that fuller details of the Cyclops are not given 

 as a means of securing a rapid acquaintance with common forms, 

 and with their later transitional stages, which occur in great 

 abundance side by side with the adults, and, like the adults, are 

 sometimes found with eggs. 



COLD SPRING HARBOR, 



LONG ISLAND, N. Y., July, 1905. 



