THE NAUTILUS. '." 



species, this 'ueing (lie dividing line between the two I'aunal regions. 

 (R.) 



In this locality the Uniones are normal in shape, but very much 

 smaller than in other places in Delaware and the neighboring states. 



i ~ o 



Adult specimens of Unio complatiatus measure 42 to 52 mm. long 

 (the normal size being 70 to 95 mm. in other Delaware streams). 



U.jisherianus is 40 to 43 mm. long, against 05 to 108 mm. at 

 Choptank Mills. 



Lampsilis cariosus, 40 to 44 mm. long. 



Lampsilis ochraceus, 40 to 50 mm. long. 



Lampsilis radiatus, 42 to 48 mm. long. 



Lampsilis n'isutus, 50 mm. long. 



The whole Unio fauna is thus dwarfed, the shells being from about 

 half to two-thirds the ordinary size. (P-) 



It has occurred to me that the dwarfing of the Unionida? of the 

 Nanticoke may be due to the fact that no tributary of this sluggish 

 river runs through a soil furnishing ingredients favorable to shell 

 growth. The relative sluggishness of this whole river system may 

 also have the degenerating effect of non-resistance. (R.) 



In the following list a few Delaware shells collected by Mr. Wit- 

 rner Stone are included, such records being duly credited : 



Polygyra tridentata (Say). Braudywine Valley between Duponts 

 and Rockland, Delaware. 



Polygyra albolabris (Say). Brandywine Valley between Duponts 

 and Rockland, and hills southwest side Brandywine near Paline, 

 Delaware. (W. Stone!) 



Polygyra thyroides (Say). Brandywine Valley between Duponts 

 and Rockland ; southwest of Brandywine Hills just below Penn. 

 State line ; and near Delaware City, Delaware. (W. Stone !) 



Polygyra hirsnta (Say). Brandywine Valley between Duponts 

 and Rockland, and near Delaware City, Delaware. 



Polygyra monodon fraterna (Say). Brandywine Valley between^ 

 Duponts and Rockland, Delaware. 



Strobilops labyrinthicus (Say). Brandywine Valley between" 

 Duponts and Rockland ; near Dover, Kent Co.; also near Delaware 

 City. 



Bifidaria contracta (Say). Near Delaware City, Delaware. 



Gircinaria concava (Say). Brandywine Valley between Duponts 

 and Rockland, Delaware. 



