548 NON-MARINE FOSSIL MOLLUSCA. 



PLATE 31. 



All the forms represented on this plate occur in the fresh- water Eocene deposits of 

 Wyoming, Colorado, and Utah ; and all are believed to be genetically related. They 

 have been described by different authors under six respective names, according to the 

 variation of ornamentation and form. (See remarks on page 464.) 



Figs. 1, 2, and 3 may be regarded as representing the Goniobasis simpsoni of Meek ; 

 Figs. 5, 10, 12, and others, G. tenera Hall; Figs. 14, 15, 20, and others, G. nodulifera 

 Meek; Figs. 19, 25, 28, and others, G. carteri Conrad; and Figs. 29 and 30, G. columlnis 

 White. Fig. 31 is a copy of Meek's figure of G. arcta, which he finally regarded as 

 only a variety of his G. simpsoni. It, is however, very like a form which occurs in the 

 Larainie beds of Bear River Valley in Southwestern Wyoming. 



