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THE AMERICAN NATURALIST [Vol. XLII 



Permian are always of small size as if they had lived in 

 particularly unfavorable conditions." The cause he 

 gives is that ''there was formed a series of interior seas, 

 soon dried up and where the excess of saltness had the 

 effect of injuring the development of the mollusks. 

 These seas have left here and there important deposits of 

 salt and gypsum." 



That this dwarfed fauna was not the normal, open-sea 

 fauna of the Permian is noted by a comparison with the 

 species of the Alps, the Mediterranean region, and India. 

 While in northern Europe the predominating forms are 

 pelecypods and brachiopods, with exceedingly few cepha- 

 lopods, in these latter more normal regions, the cepha- 

 lopods become very numerous and all are of a larger 

 size. 35 



It is interesting to note the resemblance of the fauna 

 of the Carboniferous of Windsor, Nova Scotia, to that of 

 the Permian of northern Europe. According to the de- 

 termination of de Verneuil 30 several species of brachio- 

 pods and pelecypods are common to the two regions, show- 

 ing that similar conditions tend to bring about develop- 

 ment along similar lines. 



(In this connection Schuchert's discussion of the ques- 

 tion—Is there a Permian system or only a Permian 

 formation?— is enlightening.) 37 



/. The dwarf fauna of the Cretaceous strata of New 

 Mexico and southern Colorado 38 occurs in sandy shales 

 and shaly sandstones, accompanied by innumerable frag- 

 ments of wood. Cross bedding is frequent. The ma- 

 jority of the shells are of normal size, but with these occur 

 many others which are distinctly smaller than in other 

 regions. Lima utahensis Stanton is here only one half as 

 large and Lucina subundata M. and H. is also smaller 

 than in Utah. Ostrea anomioides var. nanus Johnson is 



™ De Lapparent. Loc. cit., p. 1067. 



38 Davidson. Jour, of Geol. Soc, 1863, p. 160. 



37 A. J. 8., 22, 29-46 and 143-158, 1906. 



"Stanton. U. S. G. S. Bull. 106. Shimer and Blodgett. A. J. S., 

 25, 67. 



