llfi PALUDICELLA EHRENBERGI. 



depending solely on age and accidental circumstances of growth. I cannot think, therefore, 

 that there are sufficient reasons for considering the P. procumhcns of Hancock as distinct from 

 P. Ehrenhergi. 



I have also been unable to find, in the characters assigned by Dr. Leidy* to the species 

 occurring in the neighbourhood of Philadelphia, and named by him Paludicella ehngata, 

 sufficient grounds for the separation of the American form as a distinct species from the 

 European one. A slight difference in the length of the cells cannot afford a valid specific 

 difference, and this view is full}' borne out by the figure which accompanies Dr. Leidy's 

 paper. 



* Leidy, in ' Proc. Acad. Nat. Sci. of Philadelphia,' vol. v, p. 321. 



