A very conunon species, widely distributed and polytypic. Mature animals 

 6-18 mm long and 1-3 mm wide. Head triangular, with bluntly pointed or 

 somewhat rounded anterior tip. Auricles short and broad. Eyes normally 

 two, situated close together, anterior to the level of the auricles. 

 Coloration very variable, sometimes appearing almost uniformly brown to 

 the naked eye or composed of spots of various shades of brown with ir- 

 regularly dispersed white splotches (spotted type) ; or showing a pair 

 of dark longitudinal stripes separated by a light middorsal streak 

 (striped type), both types sometimes occurring in the same population. 

 Ventral surface usually unpigmented. Pharynx pigmented, with white 

 tip. Anatomically very similar to D. dorotooephala. Testes ventral, 

 reaching close to posterior end. Penis with round bulb and short con- 

 ical papilla directed posteroventrally. The vasa deferentia ascend to 

 the dorsal side before entering the bulb, then curve posteroventrally, 

 each widening into an elongated seminal vesicle. They unite at the base 

 of the papilla and proceed to its tip as a narrower ejaculatory duct. 

 Occasionally the lumen of the penis is expanded as a single seminal 

 vesicle, apparently a transitory condition. Bursal duct forms a rather 

 sharp angle at the entrance of the separate or united oviducts. 

 Shell glands open into the bursal duct below the mouths of the oviducts. 

 The small common genital atrium frequently shows a posterior divertic- 

 ulum. Reproduction sexual and asexual. Cocoon round, stalked. Widely 

 distributed, generally in warm ponds, lakes, and rivers in the United 

 States and southern Canada, from the Atlantic to the Pacific coasts. 

 Principal literature: Curtis (1902), Sivickis (1923), Hyman (1939b), 

 Kenk (1935, 1944). 



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