KEY TO THE ENTOMOSTRACA OF COLORADO 



277 



The males are of much the same form as the females, but much smaller. They are much less abundant 

 than the females and for some species they are unknown. The following key, based upon the characters of 

 the female, cannot be used to determine males. They are commonly distinguished from the female, among 

 other features, by the larger antennules. In most collections no males will be found, and they will seldom be 

 so numerous as to cause confusion. They can usually, with little uncertainty, be referred to the proper females 

 in the collection. 



The life-history of Cladocera is of interest. During the summer months there follow each other several 

 generations composed entirely of females. They produce repeated broods of parthenogenetic "summer eggs," 

 which are carried in the brood-chamber until the young have attained essentially the form of the 

 adult. Toward the close of the summer, or other period favorable for growth, some males are also produced. 

 At this time the females produce "winter eggs," which require fertilization. These also pass into the brood- 

 chamber where, in most forms, they are protected by special thickening of the carapace. In the Daphnidae, 

 this takes the form of a highly developed structure, the ephippium, which is shed as a protective covering for 

 the eggs. On the return of suitable conditions the eggs hatch. 



The individual species of Cladocera, unlike the Phyllopoda, as a rule have a wide geographical range, 

 many of them being essentially cosmopolitan. 



34 (37) 6 pairs of feet, all foliaceous and similar. Tribe CTENOPODA 35 



35 (36) Shell of ordinary cladoceran t3T)e. Antenna 2-branched, with many 



large setae. Family Sididae 



Dorsal branch of antenna 

 2-jointed, with a lateral ex- 

 pansion on first joint. 



Genus Latona 



Lateral expansion of first 

 joint large, reaching at least 

 to middle of second joint. 

 Length, 2-3 mm. 



Lalona setifera (O.F.M.) 



Twin Lakes, Tolland region. Never abundant. [Known in northern United States and Europe. A 

 northern and mountain form.] 



large drop of transparent jelly. Antenna un- 

 branched, with three terminal setae. 



Family Holopedidae 



Only one genus, including a single 



species. Length, to 2.0 mm. Jelly 



mass about three times the diameter 



of the body of the animal. 



Holopedium gibberum Zaddach 



Tolland region; 9,500-10,900 ft. Sporadic. 

 [From Colorado northward along Rocky Mountains. 

 Northern United States (probably in Canada), New- 

 foundland, Greenland, Iceland, Northern Europe, 

 Alps.] 



(34) 5 or 6 pairs of feet. First two 

 pairs not fohaceous but prehensile. 



Tribe ANOMOPODA 38 



36 (35) Shell inclosed in a 



■Holopedium gibberum. 



