SECTION III 

 KEY TO THE SPECIES OF NORTH AMERICAN FRESHWATER TRICLADS 



1 Anterior end triangular 2 



Anterior end truncate 7 



Anterior end rounded 35 



2 (1) Head rather acutely pointed, with prominent auricles, pharynx 



pigmented 3 



Head bluntly pointed, auricles absent or rounded, pharynx 



unpigmented 5 



3 (2) Auricles long and pointed, ventral side pigmented 4 



Auricles short, ventral side usually unpigmented: 



Dugesia tigrina (p. 20) 



4 (3) No diverticula on ejaculatory Axxzt: Dugesia dorotooephala (p. 22) 



Ejaculatory duct with a pair of diverticula: 



Dugesia antillana (p. 23) 



5 (2) Auricles rounded, penis with rounded bulb and a single seminal 



vesicle, bursal sac absent Cura foremanii (p. 19) 



Auricles absent, bursal sac developed 6 



6 (5) Penis with divided bulb and two seminal vesicles: 



Dugesia polyahroa (p. 24) 

 Penis without bulb, with rudimentary papilla: 



Hymanella retenuova (p. 31) 



7 (1) Frontal margin without adhesive organ 8 



Frontal margin with adhesive organ 28 



8 (7) Body pigmented 9 



Body without pigment, white 21 



9 (8) Eyes normally two (with occasional accessory eye spots), 



close together 10 



Eyes numerous, on margin of head (genus PoZyaelis) 19 



10 (9) Pharynx single (monopharyngeal) 11 



Pharynges multiple (polypharyngeal) 18 



11 (10) Adenodactyl present 12 



No adenodactyl present 13 



12 (11) External muscle layer of penis papilla thickened, adenodactyl 



opens into a separate chamber of the genital atrium: 



Planaria dactyligera musaulosa (p. 29) 

 External muscle layer of penis papilla not thickened, adeno- 

 dactyl opens into atrium near gonopore: 



Planaria dactyligera dactyligera (p. 28) 



15 



