314 PROCEEDINGS OF THE ACADEMY OE 



Locality and position. Higher Tertiary beds at Ham's Fork, north-east of 

 Fort Bridger, lat. 41 40' north, long. 110 c 10' west. Probably rniocene. 



Melania arcta, Meek. Shell rather small, very slender, terete ; volution? 

 about twelve, flattened convex, increasing very gradually from the apex ; suture 

 distinctly defined ; surface showing an exceedingly slight tendency to develop 

 moderately broad, rather distant vertical folds, with faint traces of small re- 

 volving striae ; aperture ovate. Length 0*56 inch; breadth 0*17 inch; apical 

 angle regular, divergence 15. 



Locality and position, same as last. 



Melaxia ? nitidula, Meek. Shell subovate ; spire conical, moderately ele- 

 vated ; volutions about six and a half, rounded convex, increasing ratber 

 gradually from the apex ; suture well defined ; aperture subovate, narrowly 

 rounded below and angular above, scarcely equalling half the entire length of 

 the shell ; surface marked by fine obscure lines of growth. Length 0.40 inch ; 

 breadth ; 0.20 inch ; apical angle convex, divergence about 40. 



Locality and position. Ham's Fork, freshwater tertiary, probable miocene. 

 Lat. 41 40' north, long. 110 10' west. 



Planorbis spectabilis, Meek. Shell large, moderately compressed ; upper 

 side slightly convex, sometimes a little concave in the middle ; periphery 

 narrowly rounded below the middle ; volutions five and a half, increasing 

 gradually in size, wider than high, depressed convex and sloping a little out- 

 wards above, distinctly convex below ; about one half of each inner whorl on 

 the under side, and less than one fourth above, embraced by each succeeding 

 turn ; umbilicus rather deep ; and one third wider than the outer whorl ; (sur- 

 face and aperture unknown.) Greatest breadth 1*19 inch ; height 0*25 inch. 



Locality and position, same as last. 



Planorbis Utahensis, Meek. Shell large, compressed discoidal, nearly flat 

 above, (sometimes slightly concave in the middle) and having a wide moder- 

 ately deep umbilical cavity below ; volutions five to five and a half, wider than 

 high, depressed and sloping outwards on the upper side, very narrowly round- 

 ed or subangular around the periphery, and convex, but not ventricose be- 

 neath ; suture rather shallow above, and deeper on the umbilical side : 

 about one half of each inner turn on the under side, and one fourth on the 

 upper, embraced by each succeeding whorl ; surface marked by fine, regular, 

 very oblique lines of growth ; aperture rather narrow, oval, and oblique. 

 Greatest breadth 1*20 inches ; smaller do., 1-07 inches ; height above 0.26 

 inch. 



Locality and position. Ham's Fork, same position as foregoing. 



LimnjEA vetusta, Meek. Shell elongate sub-ovate ; spire rather slender and 

 pointed ; volutions five and a half to six, compressed or moderately convex ; 

 suture well defined ; surface nearly smooth, with traces of fine lines of growth 

 scarcely visible without the aid of a lens ; aperture narrow ovate, rather nar- 

 rowly rounded below, and acutely angular above, equalling about half the 

 entire length of the shell ; columella with a small comparatively straight fold. 

 Length 0.56 inch ; breadth 0*26 inch. 



Locality and position, same as last. 



Limn^ea similis, Meek. Shell small, narrow subovate, or subfusiform ; spire 

 moderately elevated ; volutions five and a half to six, conxex ; suture rather 

 deep, and oblique ; surface nearly smooth or only marked by fine obscure 

 lines of growth ; aperture narrow ovate, rounded below and angular above, 

 equalling about half the length of the shell ; columella not much twisted, and 

 having a rather small fold. Length 0'39 inch ; breadth 0'19 inch ; apical 

 angle slightly convex, divergence about 38. 



Locality and position, same as preceding. 



rJuij. 



