422 E. W. Berry — Potamogeton from Upper Cretaceous. 



Named for the collector, Mr. E. S. Perry, who obtained 

 it at the Perry Place in Henry County, Tennessee, from 

 beds of Eipley age. 



This is an exceedingly well-marked species and so 

 modern in its facies as to be distingnished with difficulty 

 from numerous existing species, such as the European 

 Potamogeton riifescens, or the North American Potamo- 

 geton nuttallii, alpinus, lonchitis, and lucens. Two of 

 these latter are also Old World forms, namely P. alpinus 

 Balbis, and P. lucens Linne, and it is these two that are 

 most similar to the fossil, particularly in the shortening 

 of the petiole. Both are prevailingly pond rather than 

 stream forms, and range on this continent from the 

 Atlantic to the Pacific, and from Canada to Florida and 

 Mexico in the case of P. lucens, although P. alpinus does 

 not go so far to the southward. 



Characteristic Cretaceous forms of Potamogeton are 

 rare, and it would seem to be something more than a 

 coincidence that several well-marked species appear in the 

 geological record at about the same time in rather widely 

 separated regions. These are, in addition to the present 

 form, Potamogeton cretaceous Heer^ from the Patoot 

 beds of western Greenland — a form very similar to 

 P. perryi; Potamogeton middendorfensis Berry^ from 

 the Middendorf arkose member of the Black Creek 

 formation in South Carolina; and Potamogeton ripley- 

 ensis Berry^ from the Eipley formation in western 

 Tennessee. 



Strangely enough the genus has not been authentically 

 determined from Europe in strata earlier than the 

 Oligocene, although allied forms occur in the Eocene of 

 France. Nor are there any pre-Miocene records from 

 Asia, the last due no doubt to the scarcity of known earlier 

 plant beds on the latter continent. 



There are upward of two score described fossil species, 

 which are not uncommon throughout the Tertiary of the 

 Northern Hemisphere. Many still existing species, 

 represented by both leaves and fruits, appear in the 

 Pleistocene records. 



The existing species number more than three score, and 

 they are present in both tropical and temperate regions, 

 but are more varied in the latter. Most of the species 



^ Heer, O., Fl. Foss. Arct, vol. 7, p. 19, pi. 55, figs. 23, 24, 1883. 



2 Berry, E. W., U. S. Geol. Survey Prof. Paper 84, p. 27, pi. 4, fig. 6, 1914, 



^ In MS. 



