98 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bullion 



having the anterior portion of the ventral margin much more prominent 

 and the posterior side more contracted than others. Generally there 

 is an obscure depression extending obliquely backward and downward 

 from the posterior side of the beaks, and a stronger one passing from 

 the front side o( the beaks to the upper part of the anterior margin. 



Sometimes both Of these impressions are obsolete, while In other eases 

 they are quite distinct, and there seem to be all gradations between." 



The specimens now under consideration, two of which are figured, 

 are in the term of easts retaining only small portions of the shell. 

 They seem to agree in every respect with the types of the species, 

 although they come from a much lower horizon. 



Locality malposition. — About 350 feet above the base o( the Creta- 

 ceous section in Upper Kanab valley, Utah, where it is assoeiated with 

 many species characteristic o( the Colorado formation. Those described 

 by Dr. White came from probably the same horizon southeast of Paria, 

 Utah, and it occurs in the lower part of the Coalville section. The 

 types and all the other described specimens above referred to were 

 collected in the upper pari of the Fort Pierre shales on Cheyenne river, 

 South Dakota. 



LivlNA JTJVENIS n. sp. 

 PL XXII, Tigs. 2-4. 



Compare TAteina subundata M. & H. 



Shell small, relatively thick, moderately convex, subeircular in out- 

 line; beaks small, central, approximate; dorsal margin slightly concave 

 in front of the beaks and convex behind them: posterior end subtrun- 

 eate. the rest of the outline forming a regular curve. A narrow poste- 

 rior portion of the shell is considerably depressed. Surface marked by 

 distinct regular concentric undulations, each of which is about half as 

 broad as the intervening furrows. More numerous fine lines of growth 

 are visible under a lens. Length of the largest specimen, t>.-± mm : height, 

 gmm. convexity of the two valves united, about 3 mm . 



The specimens above described are not easily distinguishable from 

 young individuals of Lucina subundata, and if they had been found as- 

 seriated with that species they probably would not have been separated. 

 Several examples were collected, all of about the same size, and no 

 larger shells of the genus were found in the same beds with them. 



Comparison with the types of /.. subundata and with the fossils from 

 southern Utah that are referred to the same species, show that this little 

 shell has relatively less prominent beaks, its outline is more nearly cir- 

 cular, and the concentric undulations are proportionally larger. 



Locality and position.— In the Pugnellus sandstone near Malachite 

 post-office and in Poison canyon, Huerfano park. Colorado. 



