TRELEASE: THE ANCIENT OAKS OF AMERICA' 495 



a good illustration of an ample but inherently limited range of vari- 

 ation within which in the passage of long periods of time the same 

 general cycle of forms has appeared repeatedly. 



It has seemed to me worth while to arrange the principal leaf types 

 of the Cretaceous and Tertiary fossils comparatively without regard 

 to horizon ; and for convenience of reference rather than as implying 

 relationships, those of general comparability are brought together 

 by the following key: 



Leaves entire. 



Oblanceolate-obovate, large. (PI. XIII.) Magnifoliae. 



Lanceolate or oblong, moderate. (PI. XIV.) Simulatae. 



Leaves toothed. 



Teeth numerous, small and sharp. 



Leaves elongated, moderate. (PI. XV.) Fraxinifoliae. 



Leaves short and broad, small. (PI. XXII.) Spurio-ilices. 



Teeth sparse or coarse. 



Leaves broad, moderate. (PI. XVI.) Distinctae. 



Leaves elongated. 



Rather large, not pointed. (PI. XIX.) Castaneopses. 



Moderate, acuminate. (Pi. XIX, XX.) Paucidentatae. 



Small, not pointed. (PI. XXII.) Spuric-ilices. 



Leaves crenate or repand. 



Rather elongated and small. (PI. XXII.) Myricaefoliae, 



Broad, moderate. 



Some teeth acute. (PI. XVIII.) Suspectae. 



Teeth all rounded. (PI. XVII.) Dallieae. 



Leaves incised or lobed. 



Lobes or shoulders 2 or 3, toward the apex. (PI. XXII.) Bicornes. 



Lobes or divisions several, not apical. 



Leaves small, few-lobed. (PL XXI.) Lambertenses. 



Leaves moderate or large. (PI. XXI.) Lobatae. 



These foliage-groups scarcely appear to me comparable with 

 existing oaks except for the Magnifoliae, which suggest certain large- 

 leaved white oaks of Mexico and Central America; the Simulatae, 

 which may be held to resemble more or less closely some of the entire- 

 leaved black and white oaks of the United States and tropical America; 

 the Spurio-ilices, which parallel the holly-leaved black oaks of Cali- 

 fornia, and white oaks like Q. Doiiglasii, many of the scrub oaks of 

 the table-land, and the dwarf live oaks of the Gulf States; the Pauci- 

 dentatae and Castaneopses, somewhat suggestive of existing white 

 oaks with chestnut-like foliage; some of the Lobatae, comparable 

 with the white oaks of the United States which have lobed foliage, 

 as well as with some of the existing chestnut oaks; and the Lamber- 

 tenses, which resemble if they differ from existing black oaks. Of the 

 lobed forms, one only, Q. iirsina, apart from these, at all recalls our 

 familiar incised black-oak foliage to my eye. 



