^^ 



SECTION II 

 KEY TO THE GENERA OF NORTH AMERICAN FRESHWATER TRICLADS 



___ epe-^_ 



"~~~ me""" 



11- nii -|; 



-— ^^ 



epi 



A "-^ ^^ B 



Fig. 5. Muscle layers of pharynx in cross section. A, Planariidae; 

 B, Dendrocoelidae. epe, external epithelium; epi, internal epithe- 

 lium; me, external muscle layer; mi, internal muscle layer. 



1 Internal muscle zone of pharynx consists of two distinct 



layers, a circular and a longitudinal one (Fig. 5A) : 



Family Planariidae 2 



Internal muscle zone of pharynx consists of one layer of 

 intermingled circular and longitudinal fibers (Fig. 5B) : 

 Family Dendrocoelidae 9 



2 (1) Oviducts, separate or united, open into end part of bursa 



stalk 3 



Oviducts unite, the common oviduct opening into the genital 



atrium 4 



3 (2) Zone of testes extends to level of pharynx: Cura" 



Zone of testes extends to posterior end: Dugesia 



4 (2) Eyes numerous, forming a band around anterior end: .. Polyoelis 



Eyes two or wanting, if numerous not on head margin 5 



5 (4) Adenodactyl present Planaria 



No adenodactyl 6 



6 (5) Anterior end with adhesive organ : 7 



Anterior end without adhesive organ: 8 



7 (6) Body elongated, flat, with well-developed postpharyngeal 



region: Sphalloplana 



Body turtle-shaped, with reduced postpharyngeal region: Kenkia 



8 (6) Penis normal, with bulb and papilla: Phagoaata 



Penis without bulb, papilla rudimentary: Hymanella 



9 (1) Anterior end with deeply invaginated adhesive organ -.Maoroaoty la 



Anterior end with adhesive disc or without adhesive organ . . 10 



13 



