Il6 MARSH MOLIXSKS. 



Others gnaw out the pulp of fallen leaves, and thus 

 manufacture those leaf skeletons which we mid in 

 the brooks. They creep along the bottom, or up the 

 stems of plants, and occasionally they come to the 

 surface to breathe. 



The members of this family are called the Linuur- 



ida\ which means the marsh mollusks. The first of 



this numerous family which we shall consider, is 



named Potnpholyx effusa, Lea, Pom-fo'-lyx ef-fu'-sa. 



The first name means a bubble, hence we might 



expect to find that it has a thin, globular shell, as we 



really see in Fig. 103. 



f~fr. The spire is exceedingly short, and the 



m^P aperture is nearly circular and very large. 



The length and breadth of the shell are 



Fig. 103. each about one-fourth of an inch. The 



shell is horny, and sometimes it is ribbed. It is 



found in Oregon and Nevada, and there are several 



varieties which differ slightly in appearance. 



A very distinct and characteristic shell is shown in 

 Fig. .104, and bears the name of Carnifex Newberryi^ 

 Binn., Car'-ni-fex New-ber'-ry-i. 



The whorls are few and are flattened at 

 the top ; both above and below they are 

 terminated by sharp angular keels. Urn- 

 Fig. 104. bilicus large, shell thin and horny, one- 

 fourth of an inch in breadth ; from lakes. 



Gyraulus vermicularis, Gld., Ji-rau'-lus ver-mik-u- 

 la'-ris. This little species has a flattened shell, con- 

 sisting of about three rounded whorls, and is only 

 one-eighth of an inch in diameter. My specimens 

 are from Oakland, Cal. The generic name is inter- 

 esting because it was originated by Agassiz, in the 

 year 1837. The specific name was given by Dr. 

 Gould. 



