THE WATER FLEAS (CLADOCERA) 



697 



36 (37) Head not helmeted; eye close to margin. Daphnia longispina proper. 

 There are numerous varieties of D. longispina proper; depending on proportion of valves, etc. 



The head may be large or small, its ventral margin straight, concave, or convex. The eye may 

 have a large pigment with few lenses embedded in it, or it may be smaller with numerous pro- 

 jecting lenses. 

 Found in all regions of the United States. 



37 (36) Head helmeted and eye therefore removed from margin. Usually 



more delicate and transparent than 36. 



Daphnia longispina var. hyalina Leydig i860. 

 D. longispina var. hyalina varies conspicuously and greatly in the form and size of the crest 

 and of the ventral and dorsal margins of the head, which may be concave, convex, or straight 

 with any form of crest. The crest may be small and rounded (var. hyalina lypica) ; extended 

 into a broad semi-eUiptical form (form mendolae) ; more or less triangular, with an acute point 

 in front (form galeata); which may be extended into a short spine. An indefinite number of 

 other forms are present, some of which have been studied and described, but not named by 

 Entemann. The form of the crest in specimens from any one lake is fairly uniform (though 

 2 varieties may be present), changing with the season, being larger in summer than in spring. 

 Adjacent lakes may vary greatly. Deep water forms usually have smaller crests than those 

 from the shallow surface water. All varieties found in open water of lakes, in all parts of the 

 country. 



Figs. 1070, 1071 



Daphnia longispina var. hyalina, A and B, form lypica, 

 D, form galeata. 



form mendolae. 



38 (35) Ocellus absent; head helmeted. 



Daphnia longispina var. longiremis Sars 1861. 

 Valves broadly oval; spine long and slender. Head small and rounded with crest. Antennae 

 very long, reaching well toward posterior margin of valves when reflexed. Length, 9 > to i .5 mm. 

 This is the only representative of the European cucullata group as yet seen in this country. No 

 doubt other forms will be discovered. Indiana; Wisconsin, in deep water of lakes in southern 

 part of state; in surface waters in northern part. 



Fig. 1072. Daphnia longiremis. 



