COALMEASURE AND PERMOCARBONIFEROUS FOSSILS. 275 



to the beak, while the smaller are added at irregular distances; wings 

 marked b}- finer radii of nearly equal strength. A few irregular concentric 

 undulations cross the radii at unequal distances. Right valve unknown. 



This species differs from the ijreceding {A. eurtocardinalis) in the stronger 

 radii, in being higher in proportion to the width, and in the longer hinge- 

 line. It differs from A. occklarkus Meek, plate 12, fig. 13, of his report, 

 witli which it is associated, in being a smaller shell, more highly convex, 

 and in having a greater number of strong radii, with a smaller number of 

 intermediate ones; this having usually but one instead of from two to four, 

 as in that species. 



Formation and locality. — In limestone of the Upper Coal-Measures 

 (Permo-Carboniferous), foot-hills southeast of Salt Lake City, Wahsatch 

 Range, Utah. Collected by S. F. Emmons, esq. 



Genus MYALINA De Koninck. 

 Myalina aviculoides. 



Pl.ate VI, fi'r, 8. 



Myalina aviculoides M. & 11., Tioc. Acad. N. Sci. Pliil., May, 1S60, p. 184; Pal. Up. 

 Mo., p. 51, pi. 2, fig. 8. 



Shell of rather more than average size, mytilifoi-m, ovate or triangularly 

 ovate in outline, half as high again as long; beak prolonged, narrow, and 

 somewhat curved; body of the shell nearly erect, highly convex, and 

 obtusely angular along the umbonal ridge, which is placed near the anterior 

 border and parallel to it; anterior face of the shell nearly vei'tical; posterior 

 surface rapidly and regularly sloping from the crest of the ridge to the pos- 

 terior margin; hinge-line nearly as long as the shell below the prolongation 

 of the beak; anterior border sinuous above and nearly rectangular to the 

 hinge-line below; base narrowly rounded; posterior margin broadly rounded. 

 Surface marked by rather strong, concentric lines, indicating stages of growtli. 



The shell is somewhat peculiar for the form of the beak, which is slender 

 and greatly prolonged anteriorly beyond the body of the shell, with a slightly 

 upward curvature near the point. It is also remarkable for the great con- 

 vexity of the valves along the umbonal ridge, which gives an almost vertical 

 anterior face. Tliese features readily distinguish this from all other species. 



