MALAC0Z0A. GASTEROPODA. PTJUrOBRANCHIATA. 73 



skin, which covers them as a sheath ; four slender ten- 

 tacula ; the eyes situated at the tip of the upper pair of 

 tentacula ; orifice of the pulmonary cavity on the right 

 side, near the edge of the mantle ; anus opening into 

 the pulmonary aperture ; that of the generative or- 

 gans near or immediately under it ; foot very elongated. 



Shell very delicate, variously developed : sometimes 

 wanting or merely a thin scale, or agglutinated calcareous 

 grains, in the substance of the skin ; sometimes a par- 

 tially external shell, sometimes entirely external ; but 

 always very small, and incapable of containing the 

 animal. 



The species are herbivorous, feeding on the tender 

 parts of plants, on fruits, and mushrooms. They come 

 abroad chiefly in the morning and evening, or after rain ; 

 remain concealed among the herbage, or under stones, 

 or in holes, during the heat of the day ; and in winter, 

 having buried themselves in the ground, become torpid. 



Gexus 1. Arion. Arion Slug. 



Animal elongated, linear-oblong, convex above ; with 

 the mantle shield-like and granulated ; the head retrac- 

 tile, with four tentacula, of which the upper are longer 

 and oculiferous ; the mouth with an upper tooth and 

 granuliferous tongue ; the foot very large, oblong ; the 

 pulmonary cavity under the scutum, and opening near 

 its right border anteriorly ; the orifice of the anus at 

 the posterior border of that of the respiratory cavity ; 

 the genital organs united, and placed on the right side 

 anteriorly, immediately under the respiratory opening ; 

 a mucous pore at the end of the body above. 



Shell rudimentary, internal, thin, or composed of 

 calcareous particles. 



1. Arion citer. Blade Arion Slug. 



Shield granulated, cloak with numerous longitudinal 

 branched or anastomosing ridges ; upper parts black, mar- 

 gined with alternate brown and black lines, lower surface 

 greyish- blue. 



The general form oblong, flat beneath, convex above, margi- 



G 



