1898.] NATURAL SCIENCES OF PHILADELPHIA. 227 



from the table below, as all of the subfamilies are represented by 

 American genera. 



Analytical key to subfamilies and genera. 



I. Retractor muscles of pharynx and tentacles converging back- 

 ward, their posterior insertions contiguous, inserted at the pos- 

 terior edge of the diaphragm. 

 a. Tail solid, the viscera crowded forward and elevated into a 

 dorsal hump or visceral dome ; shell partly or wholly ex- 

 posed ; penis present, with retractor muscle ; ovo-testis 

 posterior in the body-cavity ; intestine short and simply 

 folded ; an accessory " retensor " muscle developed. 



Subfamily BINNEYINiE. 



b. Shell exposed, spiral, Vitrina-shaped, with differen- 

 tiated, lirate or costulate nepionic whorl ; mantle 

 with small lobes on each side of the breathing orifice ; 

 sole distinctly tripartite ; genitalia with accessory 

 organs, the penis retractor inserted on the diaphragm ; 

 -retensor muscle short, slender, toward the right side ; 

 buccal retractor shortly bifurcate anteriorly. 



BlNNEYA. 



b' . Shell partially exposed, a flat or convex, non-spiral 

 plate ; no lobes on the large mantle ; sole not in the 

 least tripartite; genitalia without accessory organs, 

 the penis retractor muscle inserted on the " retensor," 

 which is strong, wide, and to the left of the buccal 

 retractor, the latter not bifurcate anteriorly, 



Hemphillia. 

 a'. True slugs, the foot excavated throughout, the body-cavity 

 (and viscera) extending to the tail ; shell small, flat, not 

 spiral, wholly buried ; ovo-testis anterior to the posterior 

 loop of intestine ; intestine long, spirally twisted ; inner 

 cusps of outer lateral and inner marginal teeth much 

 lengthened ; pharynx retractor deeply bifurcate anteriorly. 



Subfamily ARIOLIMACLN.E. 



b. A well-developed " retensor " muscle present ; geni- 

 talia with no appendicula, the ovo-testis anterior 

 in position; tail with a "plug" in the caudal pore. 

 Large slugs. 



