526 MOLLUSCA 



Z. arborea (Say). Shell depressed, amber-colored, polished, with 5 

 whorls ; deep and narrow umbilicus ; 2.75 mm. high and 5 mm. in diam- 

 eter; head and neck black, rest of body white: entire country, the com- 

 monest species, living- gregariously under bark, leaves, etc. 



Z. minuscula (Binney). Shell depressed, with 4 whorls, with a very 

 wide umbilicus; aperture circular, with an acute lip; height 1 mm,; 

 diameter 2.5 mm.: entire United States; common. 



Z. milium (Morse). Shell depressed, with a broad umbilicus, stri- 

 ated, with 3 whorls; height .5 mm.; diameter 1.5 mm.: entire United 

 States; common. 



6. Gastrodonta Albers. Shell usually with an umbilicus, with 

 5 to 7 whorls and yellowish in color; aperture lunate, with an acute lip, 

 either with internal teeth not reaching the margin or thickened by an 

 internal calcareous deposit ; animal black, with a long dart 

 sac and mucous genital glands : 19 American species. 



G. suppressa (Say). Shell depressed, with a large 

 whorl, thin; aperture rather large; lip thickened by a 

 Fig, 817 white deposit within it and with 1 or 2 parallel ridges; 



Ugera height 5 mm.; diameter 8 mm.; umbilicus small or 



rudimentary: eastern and central states. 

 G. ligera (Say) (Fig. 817). Shell with a rather high spire; aper- 

 ture thickened within ; height 10 mm. ; diameter 15 mm. : central states. 



Family 12. LIMACIDAE. 



Slugs. No external shell present, but a rudimentary shell in form 

 of a thin calcareous plate in the mantle; body elongate and tapering; 

 mantle not extending back of the middle of the body; jaw without ribs 

 and with a median projection; ureter reflexed: about 20 genera and 

 several hundred species, which live in gardens and woods, in moist places, 

 and are nocturnal in their habits; 6 American species. 



Key to the genera of Limacidae here described: 



tti Large slugs, with spots 1. Limax 



a. Small slugs, unspotted ,2. Agriolimax 



1. LiMAX L. Body tapering and keeled behind, terminating with a 

 point; jaw with blunt ends: cosmopolitan. 

 Key to the species of Limax here described : 



Oi Spots white L. flavus 



a. Spots and blotches black , L. maximus 



L. flavns L. Color yellowish or brownish, with oblong uncolored 

 spots; body covered with long, narrow tubercles; head bluish; length 85 



