106 THE NAUTILUS. 



Pisidium mainense Sterki. 



" ventricosum Prime. 



" costatum Sterki. 



" medianum var. minutum Sterki. 



** contortum Prime. 



" triangulare Stfrki. 



*' tenuissimum Sterki. 



" splendidulum Sterki. 



" splendidulum, a new var. — Sterki. 



'* abditum ? or closely related to that species. 

 The following living shells were collected: 

 Planorbis trivolvis Say. Two specimens. 

 Planorbis parvus Say. Three specimens. 

 Anodonta fragilis Lam. One specimen. 

 Musculium sp. ? A small form, probably a new species. 

 Pisidium varinbile Prime. 



*' ventricosum Prime. 



" subrotundum Sterki. 



" mainense Sterki. 



" medianum var. minutum Sterki. 



" splendidulum Sterki. 



" splendidulum, a new variety. — Sterki. 

 As additions to the Aroostook county shells, I might mention 

 Pisidium punctum var. simplex Sterki. Dead water Caribou stream, 

 Woodland. Rare and new to the county. 



Pisidium milium Hald. is common in Gelot's Lake, New Sweden. 

 Caribou, Me. 



BEMABKS ON THE SUBFAMILIES HYBIIN^ AND UNI0NIN2. 



BY L. S. FRIERSON. 



A few facts having important bearing on the classification of the 

 Naiades, having come to notice, are herewith given to the readers of 

 Nautilus. 



Two species of the genus Pseudodon were obtained from Sowerby 

 and Fulton, showing beak sculpture. P. vondembuschiana Lea has a 

 somewhat doubly looped sculpture. The anterior loops curve upwards ; 

 the posterior are straighter, sloping backwards and downwards. 



P. walpolei has a sculpture much like that of the Cristarias, being 

 heavy bars, more or less parallel with the growth-lines. 



