17G A MANUAL OF AMERICAN LAND SHELLS. 



locomotive disk. No caudal mucous pore. Kespiratory orifice (i) snb- 

 central, on tlie rie'ht edge of the mantle, under 



Fig. 168. 



I the peristome of the shell. Generative orifice (e) 

 somewhat in the rear of the right eye-peduncle. 

 Anal orifice contiguous to the respiratory orifice. 

 Shell external, imperforate, pellucid, glassy, de- 

 pressed; spire short; whorls 2-3, rapidly increasing, the last wide; 

 aperture large ; peristome thin, often membranous. 



The jaw is highly arched, ends acuminated, blunt; anterior surface 

 smooth ; cutting margin with a prominent, beak-like, median iirojeclion. 

 I have figured the jaw of V. limpida*m Terr. Moll., V, Plate XVI, 

 Fig. H. I have found it to be the same in V. exilis and Ffeifferi. I 

 have not examined either jaw or lingual membrane in V. Angelica. 

 Fig. 1G9 gives a general idea of the lingual membrane. The centrals 

 jTio. 1(59. have a quadrangular base 



of attachment, longer 

 than broad. The reflec- 

 tion is short, with three 

 distinct cusps, the me- 



Liuguul deutitiuu of r. /i)»ijitf«. (Morse.) diau loug and Slcudcr, 



bulging at the sides, the outer ones very shor t ; all the cusps bear cut- 

 ting points in proportion to their length. The lateral teeth are ar- 

 ranged in straight transverse rows. They are like the centrals, but 

 unsymmetrical by the partial sup])ression of the inner side cusp and 

 inner lower lateral exj)ansion of the base of attachment, and the com- 

 plete suppression of the cutting point to the inner side cusp. The 

 marginals have a sole-shaped base of attachment, and truly aculeate 

 cutting points, which, however, are bluntly bifid at their iioints. The 

 marginals are in oblique, curving rows, gradually decreasing in size of 

 the teeth as they pass off laterally. They do not first increase and 

 then decrease, as in Zonites and Glandina, or not, at all events, to the 

 same degree. In V. limpida, as stated below, the seventh marginal 

 appears, however, to be the largest. 



Vitrina has a world-wide distribution. In North America it is re- 

 stricted almost exclusively to the Northern Region, excepting on high 

 elevations. 



* From Moquin-Tandon. 



