SHELLS OF LAKES AND STREAMS 313 



THE BROOK SHELLS 



{Fleuroceridcz) 



This group, distantly related to the Cerithiums of 

 the ocean, is found only in North America. Their 

 great center is in the Tennessee and Alabama River 

 Systems where several genera and a great number 

 of species are found. One genus, Goniobasis, is 

 represented by two species on the Pacific Slope, of 

 which one is common and widespread. 



Goniobasis plicifera, Lea, the Western Brook- 

 shell, PI. Ill, Fig. lo, is rather thin, slender, green, 

 brown, or black, with shallow sutures. When per- 

 fect it is nearly two inches in length, but the spire 

 is nearly always gone and the hole plugged up so 

 it has quite a stumpy appearance. In the normal 

 form the shell has smooth rounded whorls, but there 

 are a number of forms decidedly different in appear- 

 ance which have long passed as distinct species. All 

 of these the writer has found to be abnormal, due 

 to the presence of certain mineral salts in the 

 water in which they live; the different 

 forms being due to different salt constitu- 

 ents. Two of the most striking are figured 

 in Figure 297, and PI. Ill, Fig. 9. There 

 are several others. This species includes 

 G. biiJhosa^ G. nibiiiinnSiU G. aci/tifilosa, 

 G. niijrina^ G. draytoni^ G. circumlineata^ j^,. ^97 

 G. occata, and several others. 



G. pUcifera lives in swift streams and springs in 

 the Columbia and Klamath Systems. Professor 

 Keep says, "Their inhabitants are dark-skinned. 



