446 MICHIGAN SURVEY, 1905. 



treme north was more favorable to their introduction and dispersion. The 

 fact that three of the seven specimens common to both continents occur 

 fossil in the loess of Iowa, and another, Vitrea hammonis (Strom), has been 

 found associated with the remains of a mastodon in Berrien county in this 

 state, would seem to substantiate this theory. 



The following species have been found in the Post-glacial deposits in this 

 stat,e : 



Polygyra alholabris maritima (Pils). Helicodiscus parallelus (Say). 

 Polygyra thyroides (Say). Strobilops lahyrinthicus (Say). 



Polygyra monodon (Rack). Succinea retusa Lea. 



Pyramidula alternata (Say). Bifidaria tappaniana (C. B. Ads). 



Vitrea hammonis (Strom). Vertigo ventricosa elatior Sterki. 



Vitrea indentata (Say). Vertigo morsei Sterki. 



Euconulus fulvus (Dr.) Vertigo gouldii Binn. 



Zonitoides minuscula (Binn). Carychium exiguum (Say). 



Zonitoides arhorea (Say). 



III. 



HINTS ON COLLECTING MOLLUSCA. 



The collector should always bear in mind: 



First That a dead shell is better than none at all. 



Second. That dead shells should not be taken, if live ones can be had and 

 that careful search will usually discover them wherever their "bones" are 

 found. 



Third. That all the species are extremely variable in their abundance 

 from year to year, so it is a safe rule "when you're getting, to get a plenty.'' 



COLLECTING APPARATUS. 



For land shells, a "Ferriss" hoe is indispensable. This is made by get- 

 ting a small, light-handled garden hoe and having the blade cut down at a 

 machine shop. It should be about three inches Avide on top and taper to a 

 sharp point. Then cut off the handle so that it will be as long as a cane. 

 This makes a most convenient tool for turning over logs and breaking up 

 rotten wood, digging around stumps and among the dead leaves, and in a 

 snake country is very effective for killing rattlesnakes. A pair of fine curved- 

 pointed collecting forceps is also necessary for picking up the small species. 

 Small glass or wooden bottles should be carried, as the small species are apt 

 to get lost in the dirt and slime, if put into the same receptacle as the larger 

 ones. It is better not to put the small species in alcohol as they are collected, 

 as they are then killed at once with the animal more or less extended. If 

 put in a dry bottle and left a few hours they will withdraw into their shells, 

 leaving the aperture clear and fit for examination. This is especially neces- 

 sary with the Pupillidce, where the arrangement of the apertural teeth is a 

 specific characteristic. 



For the larger species tin cases of a convenient size to slip readily into the 

 coat pockets are most convenient. Where the larger Helices are so abundant 

 as to make it annoying to have to take the cover off continually, it will be 

 found convenient to have a square hole cut in the cover large enough to pass 

 a snail through. Then stretch a piece of thin rubber, such as a piece of 

 bicycle-tire lining, across the top of the can, and put the cover in place so 



