W. I. Robinson — Two New Fresh-water Gastropods. 649 



Art. XLVI. — Two New Fresh-water Gastropods from the 

 Mesozoic of Arizona ; by "W. I. Robinson.* 



In the summer of 1914, Professor H. E. Gregory of Yale 

 University collected an abundance of fresh-water gastropods 

 in northeastern Arizona. They are pseudomorphs of Si0 2 , 

 but occasionally preserving patches of the external surface 

 markings. They vary much in size and proportions, but are 

 all referable to two species, Valvata gregorii, sp. nov., and 

 Limnea hopii, sp. nov. The former species was also collected 

 by Professor Gregory in 1913 from the " Painted Desert beds," 

 chiefly Jurassic, about four miles northeast of Black Falls, 

 Arizona. Both species are closely allied to forms described 

 by C. A. White,f from beds now referred to the Morrison 

 formation and assigned by him to the Jurassic. 



In the collection of 1914, Professor Gregory also found a 

 number of TJnio fragments, apparently in the top of the 

 Triassic of the Moenkopi Valley about six miles below the 

 bridge on the Tuba-Flagstaff road. They are too fragmentary 

 for specific determination, but Doctor T. W. Stanton, of Wash- 

 ington, D. C, to whom the fossils were submitted for confirma- 

 tion of my work, states that they resemble Unio cristonensis 

 Meek, a Triassic form. 



Valvata gregorii, sp. nov. (Fig. 1, d and e.) 



Shell sub-globose : from two to three evenly rounded whorls ; 

 the first two raised in a low spire, the last increasing rapidly 

 in size and coiling obliquely to the planes of the other two. 

 Umbilicus small, but well-defined. Peristome entire; inner 

 lip somewhat reflexed. Interior surface with transverse 

 growth lines. Exterior showing in rare cases several longi- 

 tudinal ridges and grooves. Size and proportions variable. 



Smallest specimen, height 4 mm , width 6 mm 

 Medium " " 10-5 " "11 " 



Largest " " 16-5 " "18 " 



This species resembles Valvata scab rida Meek and Hayden,;j: 

 but differs from it in having fewer whorls, and a different 

 manner of coiling. 



* Published by permission of the Director of the U. S. Geological Survey. 

 •)• White, C. A., On the Fresh-water Invertebrates of the North American 

 Jurassic, Bull. U. S. Geol. Surv., No. 29, 1886. 



X Paleontology of the Upper Missouri, p. 113, pi. iv, figs. 2a, 2b, 1865. 



