MICROSCOPIC WORK. 53 



which is very minute, whitish, few-whorled and 

 lightly cancellated. 



For examining such shells a good lens is quite in- 

 dispensable, but in the hands of more advanced 

 students the minute specimens are full of interest. 



To determine the features and differences of the 

 several genera of these microscopic mollusks, one 

 should consult some recent work on conchology; 

 while to make sure of the correct specific name, the 

 most satisfactory way is to compare them with 

 authentic specimens in some good museum, or send 

 send them for determination to some one who has 

 such a collection at hand. 



We will now leave these slender, spire-shaped shells 

 and consider the Odostomias. The shells of this genus 

 are white, and are less slender in form than those of 

 the last group. They have few whorls, and on the 

 columella is a fold like a tooth, on account of which 

 they received this name, which is derived from the 

 Greek words for tooth and mouth. They are fre- 

 quently found nestling upon large shells like those of 

 the oyster and the abalone. 



Odostomia hiflata^ Cpr., O-dos-to'-mi-a in-fla^-ta, 

 has a minute white shell composed of four whorls, 

 and is about one-eighth of an inch in length. 



Odostomia Goiildu\ Cpr., is similar to the last 

 species, and is probably only a variety. It is very 

 small and has ' ' a gently-rounded base ' ' (Cpr. ). 



Odostonna gravida^ Gld., grav'-i-da, has a shell 

 minute, thin, and somewhat more slender than that of 

 the last mentioned. It is made up of five whorls. 



Odostomia nticiformis^ Cpr., nu-si-for^-mis, comes 

 next with a shell white, solid, and having a large body 



