228 PROCEEDINGS OF THE ACADEMY OF [1898. 



c. No penis nor penis retractor muscle, the vagina 

 assuming its function ; a small epiphallus ; right 

 eye retractor not passing between male and fe- 

 male branches of genitalia, Aphallarion. 

 c'. Penis large, introverted apically, with well-de- 

 veloped retractor muscle ; right eye retractor 

 involved between male and female branches of 

 genitalia, Ariolimax. 

 b'. No retensor muscle; an appendicula on the atrium ; 

 penis simple, with apical papilla and a well-devel- 

 oped retractor muscle ; caudal pore an open pit ; 

 foot-margin wide. Slugs of moderate size, 



Hesperarion. 

 II. Retractor muscles of pharynx and tentacles running parallel, 

 the latter inserted proximally at the outer posterior angles of the 

 diaphragm; (in American genera the penis and its retractor 

 muscle wanting, the free oviduct or the vagina assuming its 

 function) ; epiphallus variously modified. True slugs, with com- 

 pletely buried shell plate or vestige, and visceral cavity extend- 

 ing into the tail. 



Subfamily ARIONIN^E. 



a. Retractor muscle of the pharynx inserted proximally de- 

 cidedly behind the posterior edge of the diaphragm ; intes- 

 tine long and strongly twisted spirally, the stomach, or 

 posterior loop formed by G 1 and G 2 , lying behind the loop 

 formed by G 3 and G*; kidney ring-like, exposing both 

 chambers of the heart from below. 



b. Epiphallus slender, tapering distally, not abruptly 

 bent or constricted near the atrium ; spermatheca 

 duct inserted upon the atrium; free oviduct func- 

 tional as a penis; ovo-testis extending behind the 

 intestine ; external integument longitudinally rugose ; 

 sole more or less visibly tripartite ; a mucous gland 

 at the tail ; breathing pore decidedly anterior to mid- 

 dle of mantle, the genital orifice below it, Arion. 

 a'. Retractor of the pharynx inserted at the posterior edge of 

 the diaphragm ; intestine shorter, not much twisted spir- 

 ally, the stomach, or posterior loop formed by G 1 and G 2 , 

 lying far anterior to the posterior loop formed by G 3 and 

 G 4 ; external genital orifice anterior, near right tentacle. 



