LAND AND FRESH-WATER SHELLS OF N. A. [PART IV. 



Fig. 25. 



Description. — Shell fusiform; base canaliculate; spire ele- 

 vated ; columella smooth and concave. — Lea. 



GeograpJiical Distribution. — The 

 few species comprising this genus 

 appear to inhabit exclusively the 

 waters, of Middle and East Ten- 

 nessee and southwestern Virginia. 



Observations. — Mr. Lea has re- 

 cently described eight species which 

 he proposes to consider a distinct 

 group of /o, but I cannot distinguish 

 them from Pleurocera. The longer 

 fuse, sharp lip and fragile texture of 

 most of these species, show them 

 to be immature shells, and in several 

 instances I had no difficulty in proving them identical with 

 mature shells described by Mr. Lea as Trypanostoma {zn Pleu- 

 rocera)^ by means of series of specimens of different ages. 



Excluding these, twelve species have been described ; of 

 which we propose to retain five, regarding the others as syno- 

 nymes. Many naturalists consider the genus to be restricted 

 to one valid species, and cite the nearly uniform size of the 

 shells, their similar ornamentation and restricted habitat as 

 proofs of the correctness of their opinion ; there appears to me 

 to be a well-founded division of the species into two groups, 

 the one containing shells which are smooth or obscurely tuber- 

 culate, and the second those developing distinct spines. En- 

 deavors have been made to connect lo Jluvialis and spiinosa, 

 the respective types of the two groups, by series of specimens, 

 but no Jluvialis has been found with better developed protu- 

 berances than the shell described by Mr. Reeve as vemicosa, 

 which is still a long way from the spinosa. In the 3'oung 

 shells the differences are very much better shown than in 



