JUKASSIC SPECIES. 133 



senting Sowerby's species. In one important cliaractor, however, onr sliell 

 certainly differs, at least from the lignres published Ijy both of the above- 

 mentioned authors; that is, in the great regularity of its concentric striaj. If 

 I knew their figures to be exactly correct in this respect, I should not hes- 

 itate to regard our shell as belonging to a distinct species; but, until this 

 question can be settled by a comparison of specimens, I prefer to view it as 

 a variety of Sowerby's species. In the fineness and regularity of its striae, 

 as well as in its remarkable thinness, it agrees with V. pertenids, M. & H., 

 from the Jurassic beds near the Black Hills; but, in addition to being much 

 larger, it is more arcuate, and has more prominent undjonal ridges; while 

 its anterior ventral region below and in front of the mubonal ridge is pro- 

 portionally larger. It is barely possible, however, that these may not be 

 constant characters. 



Locality and position. — Weber Canon, Wasatch Range, Utah; Jurassic. 



TEIGONllDyE. 



Genus MYOrilORIA, Broun. 

 Myophoria line ATA, Mulister?. 



Pl.ito I'J, ligs. 3, .3 a. 



Trigonia Uneata, IVIiiiister (1834), Leonhard unci Broim's Juhrl)., I, .5 and 1). 

 Lyrodon Uneatum, Goldf. (1838), Tetref. Germ., II, I'M, tab. 13G, tigs. 4, a, b, c, d. 

 Myophoria Uneata, Miiuster (1841), Beitnige, IV, 88, tab. 7, fig. 29; and (1804) in 



Alberti's, Trias, 111.— Laube (1805), Fauna St. Cass., 59, tab. 18, fig. 7. 

 Trigonia Uneata, Gie.bel (1852), Deutscbl. Pctref., 392. 

 Opis Uneata, Laube (18(U), Beraerk. im Jabrb. d. Geol. Eeichsaust., 489 ; Fauna der 



Schicht. von St. Cass., 59, pi. xviii, fig. 7. 



Shell small, trigonal, rather compressed; anterior end shorter than the 

 other, rounding from below the beaks into the base; posterior side com- 

 pressed, truncated, with a slight forward slope above, and angular at the 

 base; ventral margin semiovate, rounding up anteriorly, most convex in out- 

 line slightly in advance of the middle, and straight or very slightly sinuous 

 near where it connects with the posterior basal angle; beaks apparently 

 elevated, and placed a little in advance of the middle ; posterior umbonal 

 slope forming a well-defined angular ridge extending from the back part of 



