854 Notes on a Nevada Shell ( Pyrgula nevadensis). (September, 
The formula for the denticles is 30~24~7—" tit 4 7-24-30. i 
There is a marked variation in the character of the denticles on the intermediate 
and lateral teeth. On the intermediate they are large, angular and somewhat irreg- 
ular. The lateral teeth are uniformly marked by a regular fringe of slender denticles, 
which are much smaller on the outer lateral. 
Some portions of the membrane and different specimens show considerable varia- 
` tion in the length and strength of the denticles on the lateral teeth, and sometimes 
their number seems subject to some mutation. The numbers given in the formule 
were averaged from several enumerations, and represent the comparative denticula- 
tion of the teeth, 
Lingual dentition of Pyrgula nevadensis Stm., X 500 (Beecher). 
DESCRIPTIONS OF FIGURES. 
Fic. 1.—Rhachidian teeth. 
Fic. 2.—Intermediate teeth. 
IG. 3.—Inner laterals, | : 
Fic. 4.—Outer laterals, their natural a 
Fic. 5.—A portion of the odontophore representing the wekt 
tion. All enlarged to 500 diameters, 
