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UNIVERSITY OF COLORADO STUDIES 



are to withstand another period of dryness. They are of sporadic occurrence, being found only in certain 

 pools in a locality, and in them not every year. Under favorable conditions they may crowd a pool in enormous 

 numbers. Most species of Phyllopods have a very limited range. Of the 42 species known from North 

 America, almost all are confined exclusively to that area. Of the 42 North American species, 16 have been 

 reported from Colorado, and 25 of them are confined to the states west of the meridian of Kansas City. In 

 the semi-arid plains of this region, which seem to offer specially favorable conditions for Crustacea of this 

 type, they form a larger part of the Entomostracan fauna than in other parts of North America. The relatively 

 small amount of exploration, and the probability that future work will add considerably to the number of 

 species from this region, place further emphasis on the importance of this part of the aquatic fauna of the 

 great plains. 



Most of the Phyllopods hatch as a nauplius (Fig. 61), a small swimming larva with an unpaired eye and 

 three pairs of appendages (ist and 2d antennae and mandibles), or as a metanauplius with the beginnings of 

 segmentation farther back. The males of most species are much less abundant than the females and for some 

 species they are unknown. In many species parthenogenesis is by no means uncommon at certain times. 



3 (13) Carapace wanting. Body elongated. The "fairy shrimps." 



Order Anostraca 4 



AH of ours have 11 pairs of swimming feet. Usually swim on back. Second antenna of male always 

 large and used as a clasping organ, which is important in distinguishing species. Corresponding organs in 

 the female are small and do not differ greatly in different species (Figs. 2-8). 



4 (10) Clasping antenna of male 2-jointed 5 



5 (9) Head of male with no frontal process. All of ours have 9 posterior 



segments without limbs Family Branchinectidae 



Genus Branchinecta 6 



6 (7, 8) Basal segment of male clasping antenna imarmed on inner margin, 



except for a swollen, spiny area near the base. Length: male, 13.6; female, 

 12. 8 mm Branchinecta lindahli Fa.cka.Td 



Greeley; 4,600 ft. [Kansas, Nebraska, Wyoming.] 



Fig. 2. — Branchinecta lindahli. 

 Male. (After Shautz.) 



Fig. 3. — Branchinecta colora- 

 densis. Male. 



7 :^- (6, 8) Inner margin of basal segment of male clasping antenna with an 

 elevated spiny area near middle and a prominent tubercle near the base. 

 Length: male, 18; female, 17 mm. . Branchinecta coloradensis Fa.cka.id 



Abundant in mountain regions of Colorado, especially above 11,000 ft. Has been considered a type 

 of a strictly alpine form, but material collected by Ellis at St. Vrain (5,100 ft.), well outside the mountain 

 area, contains specimens which I would without hesitation refer to this species, were they collected in the 

 mountains. 



