LOGAN: FREEZE-OUT HILLS OF WYOMING. 133 



has not been recognized in any older formations. It occurs here in 

 apparently the same degree of development, and has not been recog 

 nized m any older rocks on this continent. 



Vitio If UN. stout, n. sp. Plate XXXI, %. 10. 

 Shell medium size, broadly subelliptical but only slightly convex 

 The ventral border of the shell is nearly straight while the dorsal 

 border is moderately convex. The posterior margin is sharply 

 rounded -. the anterior margin is subtriangular. The test is thick 

 The surface of the shell is ornamented by prominent concentric lines 

 of growth. The convexity of the surface is slight and has its greatest 

 prominence in the umbonal region. The ventral slope is short and 

 abrupt while the dorsal slope is long. 



Dimensions: Length, oO mm.; uddth, 30 mm.; convexity, 5 mm 

 Greological horizon : This species occurs in No. 22, associated w^tli 

 other non-marine forms. 



Locality : The Freeze-out Hills, of Wyoming. 

 _ Remarks : The type specimen is a cast of a large individual, which 

 IS the largest .specimen collected. 



The genus rnio was first recognized in the Wealden of En-dand 

 ■where it occurs in about the same degree of development as in the 

 Atlantasaurus Beds. The appearance in these two formations of four 

 genera, occurring for the first time and in practically the same degree 

 .ot development, furnishes a strong argument in favor of their correla- 

 Ition. 



I ahfita Icei, n. sp. Plate XXXI, figs. 1, 2, 3. 

 Shell small, composed of three volutions, which increase rapidly in 

 e The spire is depressed so that it does not equal more than one- 

 lialt the body whorl at the aperture. The test is very thin The 

 . olutions are subangular around the upper outer side, and flattened 

 ...nzontally between the angle and the suture; ventricose on the 

 .uter and under sides. The suture line occupies a well-marked de- 

 n-ession. The aperture is oval in shape. The surface is ornamented 

 )y prominent lines of growth. 



Dimensions: Diameter through aperture, L3 mm.; diameter ex- 

 •lusive of outer whorl, 4 ram.; height of spire, less than 3 mm.; 

 1 eight of outer whorl at aperture, 4 mm. 



Geological horizon : No. 22 of the section, where it is associated 

 . ith species of Unio and Lioplacodes. 

 Locality : The Freeze-out Hills, Wyoming. 



Remarks : The type specimen was collected from the above stratum 

 y Mr. W. T. Lee, in whose honor it is named. It is not as large a 

 liell as Yalvata scrihda, described by Meek, from Dakota, but it 

 iffers more essentially in the character of its spire, which is much 



5ize. 



