52 THE NAUTILUS. 



51. Pisidium Dabneyi De Guerne. Kindness Mr. Dabney. 



52. Pinna rudis L. 



Where no locality is mentioned in the list, Horta, Fayal Islands, 

 Azores, is to be understood. 



NOTES ON FAMILIAR MOLLUSKS. 



BY W. M. BEAUCHAMP. 



It is the custom to call Melantho rufus Hald., a variety of M. 

 decisus Say, and there are some good reasons for this. It is more 

 than a mere color variety, however, as those familiar with its habits 

 know very well. The shell is usually grayer and moi'e polished 

 without, besides the rich purple within. It requires warmer water 

 than 31. decisus, and in New York is restricted to favorable localities, 

 while the other has a very wide range. Those who have taken the 

 animal from the shell, find that it has a greater muscular adhesion, 

 not separating readily. The young mollusks have well marked 

 features from the very first. Thus far in New York, I have found 

 the shell only Avhere canal boats have been. 



Some have also thought Valvata tricarinata and sincera Say, 

 varieties of one species. There is little to suggest this in the forms 

 or habits of these little shells. The outer appearance is very differ- 

 ent, they have not the same haunts, nor do they eat the same food. 

 If they are ever found together, it is in death rather than in life, as 

 far as my experience goes. 



Bythinia tentaculata Linn, has become very abundant since I 

 first reported it many years ago. In portions of the Erie Canal it 

 has driven out Goniobasis llveecens and Vlrgiaica, merely by eating 

 up their food. It prefers canal waters to any other, as many species 

 do. 



In the Erie Canal I collected Pleurocera suhulare Lea, but with 

 this I found P. intensiun and paUidum, of the same author, which 

 seem only varieties of the former. Mr. Tryon agreed with me in 

 this. The variations are by no means as great as in Gon. Virginica 

 Gmel. ; in fact there seems little difference beyond the color and mark- 

 ings. 



I have had Margaritana margaritifera Linn from tributaries of 

 the Mohawk river, but nowhere west of these in New York. It is 



