Beede.] Carboniferous Invertebrates. 139 



Myalina ampla. Plate XVI, figs. 1, lb. 



Myalina am phi Meek and Hayden, Pal. Upp.jMo., p. 33, ff. A, B, (1864). 

 Myalina subquadrata Meek and Hayden, ibid., p. 32. 



Meek and Hayden's description : " Shell attaining a large size, 

 compressed and somewhat alate in the postero-dorsal region, and 

 convex anteriorly — considerably higher than long; posterior 

 margin forming a broad gentle curve, being nearly straight and 

 ranging almost vertically near the middle, and curving forward 

 so as to intersect the hinge at an obtuse, undefined angle above, 

 while below it arches regularly forward into the rather narrowly 

 rounded base ; anterior margin thickened within above, broadly 

 arcuate or concave in outline, its curvature being nearly paral- 

 lel to that of the posterior margin. Beaks terminal, directed 

 forward ; umbonal ridge most prominent and oblique above, 

 and in adult shells curving downwards so as to range nearly 

 vertically near the middle. Hinge line straight, and ranging 

 nearly at right angles to the longer or vertical axis of the 

 valves ; cartilage furrows distinct, straight, and in mature shells 

 numbering about ten or twelve ; area broad. Height, about 4 

 inches ; antero-posterior diameter at the middle, 2.40 inches ; 

 convexity of a left valve, 0.83 inch." 



Range and distribution : Upper Coal Measures ; the type 

 specimen was collected at Leavenworth. 



There is one specimen in the collection from the type locality 

 which probably belongs to this species, the only difference 

 being that the lines of growth do not bend quite so sharply 

 forward as in the ones figured by Meek. The principal differ- 

 ences between this shell and M. subquadrata are : Very convex 

 posterior outline instead of a straight or concave outline, greater 

 size, and the curving forward of the lines of growth. 



Meek was in doubt as to whether it was the same as M. sub- 

 quadrata of Shumard or not. He proposes the name at the close 

 of the description of the shell, and comments upon it, stating 

 that he is of the opinion that it is a distinct species. Later, in 

 the final report on Nebraska, he states, in the discussion of M. 

 subquadrata (page 203) : "The large species figured by Doctor 

 Hayden and the writer on page 33 of the Paleontology of the 



