186 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Inhabits all of the Eastern, Central, and Pacific Provinces, having been found 

 from Gaspe to Texas ; on the Rio Chama, New Mexico ; in Idaho ; in Oakland, 

 California. 



Jaw : see p. 1 84. 



Lingual membrane : see p. 184. 



Animal (see p. 184) nearly white or rather translucent, mottled with small 

 white blotches; body long and narrow; upper posterior portion of foot con- 

 spicuously furrowed. In motion the shell lies perfectly flat on the extreme 

 posterior portion of body, the eye-peduncles standing nearly perpendicularly, 

 and the head with tentacles thrust out some way beyond the base of eye- 

 peduncles ; eyes scarcely visible ; animal very short posteriorly. 



This peculiar shell is distinguished by its discoidal form, greenish color, the 

 fine revolving lines upon its whorls, and the singular teeth which are placed in 

 the interior of the outer whorl. These teeth are arranged in pairs, on the ex* 

 ternal side of the parietes of the cavity, one of each pair being on the superior 

 and one on the inferior part of the whorl. They are prominent, white, and 

 conical, and may be discovered through the semi-transparent shell. One pair 

 is so near the aperture as easily to be seen, on looking into it; the other is dis- 

 tant nearly one half a volution from the peristome, and is of course invisible 

 except through the shell. At least one pair will be found to exist in every 

 specimen, when carefully sought for ; in one instance, I noticed a third pair 

 still further within the whorl. 



Noticed under the bark, or in the interstices of wet and decaying wood, and 

 under layers of wet leaves and stones, in damp places, in forests. 



FERUSSACIA, Risso. 



Animal heliciform, as in Palula, obtuse before, pointed behind ; mantle sub- 

 central, thin, simple, protected by a shell ; anal and respiratory orifices on the 



right of mantle, under the peristome of the shell ; gen- 

 Fig. 93. erative orifice behind the right eye-peduncle ; no loco- 

 motive disk ; no caudal mucus pore. 



Shell ovate-oblong, imperforate, smooth, pellucid, 

 glistening, dark horn-colored ; whorls rather convex ; 

 aperture less than one half the shell's length, ovate ; 



Animal of Ferustacia , 



(Reeve). columella more or less truncated ; peristome blunt, its 



margins joined by callus. 



The genus seems most developed around the Mediterranean Sea, but it is 

 found also in Madeira and Australia. Our only species is circumpolar. 



The jaw is low, slightly arcuate, wide, with but slightly attenuated, blunt 

 ends; cutting edge with a slightly produced, wide, median projection; anterior 

 surface without ribs, but with fine vertical strife. There is a strong muscular 

 attachment on its upper margin. (See Fig. 94.) 



