90 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull. 106. 



stones at Boar Kiver city, Wyoming, and Prof. Meek recognized the 

 species in sandstone near the base of the section at Coalville, Utah, in 

 the same layers from which the types of Barbatia coalvillensis were ob- 

 tained. A study of all these types and of large collections from the 

 same localities has convinced me that they belong to a single species, 

 and that the smaller shells called "Macrodon (undetermined sp.) w by 

 Meek are the young of the same species. 



White's revised description of the Coalville specimens is as follows: 



"Shell not large, moderately gibbous, transverse length from two- 

 fifths greater to nearly twice as great as the height; beaks depressed, 

 situated near the anterior end ; umbones broad, not prominent; anterior 

 end rounded or subtruncate; base usually nearly straight, but some- 

 times slightly convex and sometimes a little einarginate about the mid- 

 length ; postero-basal border rounded upward to the posterior extremity, 

 which is abruptly rounded up to the downward sloping, nearly straight 

 postero dorsal border, the latter forming a rounded obtuse angle with 

 the cardinal border ; hinge equal in length to about two-thirds the entire 

 length of the shell, consisting of a moderately slender hinge plate bear- 

 ing numerous transverse teeth with about equal spaces between them. 

 The posterior teeth have an oblique direction downward and a little for- 

 ward, which obliquity diminishes towards the front, so that the teeth 

 from about mid length of the hinge to the center of the beak are directly 

 transverse. These central transverse teeth are a little narrower than 

 those farther back, but the two or three teeth in front of the center of 

 the beak are larger than any of the others, and a little curved. 



"Area apparently nearly obsolete, or at least it is very narrow. 

 Internal markings unknown. A slight depression or flattened space 

 upon the outer surface extends from the umbo of each valve to its 

 base, meeting there the straight or slightly emarginated portion of the 

 basal margin before mentioned. 



"Surface marked by the ordinary lines of growth and also by fine 

 radiating lines, which are often obscure. 



"Length of an example a little above the ordinary size, 5 r,n ; height, 



Additional material from the original locality shows that in adult 

 shells the hinge line is curved downward at each end and in these 

 curved portions the teeth are large, slightly curved, and oblique to the 

 hinge line, those at the extreme ends, especially the anterior one, 

 becoming almost parallel with it. The medial portion of the hinge is 

 not so well preserved in any of the specimens, but there are obscure 

 impressions of small, closely arranged, transverse teeth. The liga- 

 mental area is narrow, with two or three Avell-defmed grooves, poste- 

 rior to the beak and nearly parallel with the hinge. These features 

 arc all made out from easts and impressions in sandstone. 



In the Timber Creek beds, near Lewisville, Denton county, Texas, 



