460 G. R. Wieland — Origin of Dicotyls. 



a continual growth of new plants, they better withstood cold and 

 quickly grew over and out beyond all their essentially conserva- 

 tive competitors. Thus was alike displaced first the cycado- 

 phytan underbrush and then the great coniferous forests of 

 the early Cretaceous. And thus do we also h'nd inescapable 

 ecologic reasons why the paleontologic record reflects true con- 

 ditions in so universally suggesting a most rapid spread of 

 angiosperms over the globe following extensive polar develop- 

 ment of the more characteristic initial types in the late Jurassic. 



Peabody Museum, Yale University, 

 New Haven, Conn. 



Art. XXXIX. — Unios in the Triassic of Massachusetts ; 

 by Edward L. Troxell. 



Among the Triassic specimens of Amherst College Museum 

 there is a unique slab of sandstone containing several casts of 

 fresh-water pelecypods, apparently of the genus TJnio. This 

 slab came from the Upper Triassic at Wilbraham, Massachusetts, 

 and was the gift of Mr. Charles S. Merrick. 



Professor Emerson has figured and described the best cast 

 on this slab as AnopJophora wilbraha?nensis* and the writer 

 has developed the other casts and found that two species are 

 present on the slab. At the time of Professor Emerson's 

 publication, he appears to have regarded these bivalves as of 

 possible marine origin and accordingly referred them to the 

 genus A?ioplophora, whose species occur in the brackish-water 

 deposits of the Triassic of Germany. It is true that these 

 German forms, at least in name, are usually associated by 

 authors with fresh-water bivalves, but as they are found in 

 association with a brackish-water fauna it is very probable that 

 Anoplophora cannot be extended to embrace the American 

 shells. While the latter cannot be definitely referred to Unio, it 

 can be said that the Triassic of eastern North America has not 

 yielded a single marine animal, while all the physical evidence 

 points to its continental character. 



Zittel says that Anoplophora is thin-shelled, is not bellied, 

 and is without teeth, characters which are in strong contrast to 

 those of the Massachusetts specimens. 



U. emersoni, n. sp. (fig. 1). — The most striking features of 

 this species are its elongation and narrowness, though these 

 *This Journal, (4),. x, p. 58, 1900. 



