122 



LAND AND FRESH-WATER SHELLS OF N. A, [PART I.' 



shape in the larger. The coloring exhibits every shade, from 

 light amber to dark chestnut. The whirls of some revolve about 

 the axis at such a distance as to leave a deep and wide umbilicus 

 (nionodon) ; while in others they are in such near approximation 

 as to permit only a small perforation, which the narrow, reflected 

 peristome is sufficiently wide to cover {fraterna). The hairy 

 projections of the epidermis are most distinct upon the young 

 shells, but are often wanting at every stage of growth. The 

 oblique striae are so fine as hardly to be visible ; and in some 

 instances the shell appears to be glabrous. Yery beautiful 

 specimens, about one-fourth of an inch in diameter, with a dark, 

 shining epidermis and open umbilicus, occur in Ohio, Indiana, 

 Iowa, and Michigan. They are more convex, and, as the same 

 number of volutions is contained in half the space, they appear 

 to have more whirls than the common variety. Some persons 

 have considered these to form a distinct species (H. leaii, Ward, 

 MSS.) ; but I do not see that they can, with propriety, 

 be separated. 



Fig. 203 is drawn from a curious pathological speci- 

 men. The peristome having been broken after the 

 animal's arrival at maturity, a new peristome has been 

 formed somewhat in the rear of the first, and a new 

 parietal tooth added. The base of the shell was pur- 

 posely broken to show the position of the internal tubercle. 



The jaw of H. vionodon is slightly arcuate, 

 stout, bluntly rounded at ends ; anterior sur- 

 face with' broad, stout ribs denticulating each 

 margin. 



Lingual membrane with 100 rows of 

 28 — 1 — 28 teeth each; centrals and laterals 

 stout, with a short, pointed apex ; uncini 

 irregularly furnished with long denticles. 



Fie- 204. 



Jaw of Helix monodon 

 [Morse.] 



Fig. 205. 





LiDgual deotUioa of fielin fnonodoji. [Mouse] 



