112 



THE AMERICAN NATURALIST 



[Vol. XLIT 



2. North American Migrations of certain Creodonta 

 (Pachyaena, Palaeonictis). 



III. Loiver Ypresian stage (beds of the London Clay, 

 Heme Bay, Kyson, Harwich, Isle of Sheppey, in Eng- 

 land; beds of Pourcy near Reims in France). Fauna 

 little different from that of the preceding stage. 



1. Local Evolution.— Continuance of Amblypoda (Co- 

 ryphodon), and of Hyracotheriidae (Hyracotherium). 



2. Migration of North American Origin of the Tillo- 

 dontia ( Platychaerops = Esthonyx ) . 



IV. Upper Ypresian stage (beds of Teredo-sands, Ay, 

 Cuis, Chavot near Epernay). 



1. Local Evolution. — Continuance of Insectivora (Ada- 

 pisoriculus), of aberrant Primates (Plesiadapis), of Creo- 

 donta-Mesonyehidae (Hyaenodictis = Dissaeus), and of 

 Hyracotheriidae ( Propaehynolophus ) . 



2. Important Migrations, Probably of North American 

 Origin, of the mesodont Primates (Notharctidae, genus 

 Protoadapis), of the Rodentia-Pseudosciuridae (Dectica- 

 dapis), and Sciuridae (Plesiarctomys), of Lophiodontidae 

 (parallel branches Lophiodon and Chasmotherium), of 

 the Paridigitate Suillines (Protodiehobune) and perhaps 

 of Titanotheridae (Brachydiastematotherium). 



This horizon is marked by some important migrations 

 and great changes in the mammalian fauna, in conse- 

 quence of which the latter approximate more closely to 

 the fauna of the middle, than to that of the lower Eocene. 



V. Lutetian stage, two successive faunae: 



(a) Lower and middle Lutetian (beds of Argenton, 

 of Bracklesham and part of the 4 4 terrain siderolithique" 

 of Egerkingen and of Lissieu). 



Local evolution of Lophiodontidae (Lophiodon, Chasmo- 

 therium), of Hyracotheriidae (Pachynolophus, Propalaeo- 

 therium) and of Dichobunidae (Meniscodon, Dichobune). 



(b) Upper Lutetian ("Calcaire grossier" beds of 

 Paris: Xanterre, Vaugirard, Gentilly; Coucy, Dampleix; 

 of Buschweiler, of Issel ; les Matelles, St. Gily du Tesc ; 



