MUSEUM OF COMPARATIVE ZOOLOGY. 155 



absence of limestone on Roan Mountain accounts for the extreme thinness of 

 the shell. 



It can scarcely be said to resemble closely any known species of Mesodon, 

 though perhaps somewhat like a gigantic M. Mitchellianus. 



The jaw has sixteen ribs. 



The lingual membrane (PI. III. Fig. F) is long and narrow ; teeth 64-1-64, 

 with about 15 perfect laterals on either side of the central line. There are no 

 side cusps or cutting points to the central and lateral teeth, and only on the 

 extreme marginals does a side cutting point appear. The cutting point of the 

 marginals is long. Thus the dentition is like that of dausus and thyroides. 



The genitalia are figiu'ed on Plate III. Fig. E. The genital bladder (g. b.) is 

 large, oval, on a short, narrow duct : the penis-sac (j). s.) is long and stout, with 

 a subcentral constriction : the prostate gland (pr.) is highly developed. 



A dentate form is figured on Plate IV. Fig. A. 



Mesodon Wheatleyi, Blaxd. (p. 327.) 



Roan Mountain, Mitchell Co., North Carolina ; Cliff Springs, Monroe Co., 

 Tennessee. Mrs. G. Andrews. The parietal tooth was wanting in these 

 specimens. 



Mesodon dentiferus, Binnet. (p. .328.) 



Plate III. Fig. G. 



On Plate III. Fig. G, I have figured the genitalia of this species. 



The genital bladder {g. b.) is small, oval, on a short duct, which is greatly 

 swollen at a short distance below the bladder : the penis-sac (p. s.) is long, 

 stout, and contracted at a short distance below its blunt end ; the retractor is 

 inserted in the vas deferens at about the middle of its lencrth. 



In another individual, the constriction of the penis-sac was not so well de- 

 veloped. 



Mrs. G. Andrews found at Sugar-Loaf IMountain, North Carolina, twenty 

 miles east of Roan Mountain, a specimen of 5j whorls ; greater diameter, 

 30 mm. ; lesser, 25 mm. ; height, 12 mm. 



Mesodon Wetherbyi, Blaxd. (p. 330.) 



Roan Mountain, Mitchell Co., North Carolina ; Campbell Co., Tennessee, 

 Mrs. G. Andrews. Animal uniform slate-color. 



Mesodon clausus, Say. (p. .3.32.) 



Helix InqaUsiana. See Fischer, in Simttle worth's Notitia; Ma!., II. 10, PI. III. 

 Fig. 5 (1877). 



