pilsbe-t: phtlogent of aeionid^. 101 



d. No penis, its function shifted to the vagina. 



Aphallaiion. 

 d' . Penis large, introverted apically, with large retractor. 



Ariolimax. 

 c'. '^0 retensor muscle ; ovotestis behind stomach ; an appen- 

 diculum on the atrium. Sesper avion. 



B. Retractor muscles of pharynx and tentacles running parallel, the 

 posterior insertions of the ]atter widely separated on the 

 posterior margin of the diaphragm (PL YII, Fig. 1). True 

 slugs with a small, flat internal shell plate, or vestige, and 

 long visceral cavity. 



Subfamily Aeionin^. 



h. Pharynx retractor inserted at the posterior margin of diaphragm; 



second posterior loop of the intestine extending far behind 



the first loop. 



c. Penis well developed, with normal retractor ; intestine 



rather long, twisted; foot-margin extremely narrow; 



no caudal gland ; sole not distinctly tripartite. 



Anadenus. 

 c' . No penis, its function assumed by the vagina ; intestine but 

 slightly twisted ; caudal gland small or none. 

 d. Sole not in the least tripartite ; end of tail subject 

 to self-amputation ; epiphallus more or less swollen, 

 suddenly constricted before entering the atrium ; 

 both chambers of the heart exposed. Propliysaon. 

 d' . Sole tripartite, the narrow median field defined by 

 longitudinal grooves; tail normal; kidney concealing 

 the auricle. (Genitalia unknown.) Anadenulun. 

 y . Pharyngeal retractor inserted decidedly behind the posterior 

 margin of the diaphragm ; intestine long, twisted, the first 

 posterior loop extending well behind the second ; no true 

 penis ; a small caudal gland. 

 c. Shell more or less incoherent ; genital orifice posterior, 

 below the breathing pore; epiphallus tapering; sperma- 

 theca duct inserted on atrium, the oviduct functional as 

 a copulatory oi'gan, with a retractor muscle. Arion. 

 c'. Shell strong, thick ; genital orifice anterior ; integument 

 laterally expanded, free and overhanging the sole 

 posteriorly. Letourneuxia. 



c". Shell strong, solid; genital orifice anterior; atrium pulled 

 out into a long sack carrying the spermatheca and 

 epiphallus, and functional as a copulatory organ. 



Geotnalacus. 



The arrangement of genera proposed above is graphically repre- 

 sented in the following diagram, which is intended to represent the 

 phylogeny of the group. As might be expected, none of the more 

 primitive genera stand directly in the line of descent, although 



