10 



ORDER ASIPHON1DA. 

 Family XRGIDM. 



MACRODON FACETUS, n Sp. 



Plate I, Fig. 14, cardinal view; Fig. 15, right valve, both ends 

 of the specimen are broken; Fig. 16, surface oj the 

 cast magnified six diameters. 



Species small Our specimens are casts but part of the surface 

 markings of the shell are preserved. Shell elongate, about or 

 more than twice as long as high; highest about the anterior third. 

 Valves convex and thickness about equal to the height. Cardinal 

 line straight and a little short of the greatest length of the shell. 

 Anterior end angular at the cardinal line and then rounded in'o 

 the basal margin. Posterior end obliquely truncated, from the 

 end of the cardinal line, and then narrowly rounded, at the post- 

 basal extremity, into the basal margin. Basal margin broadly and 

 somewhat evenly rounded. Beaks near the anterior end and in- 

 curved above the hinge line. Umbones prominent and fading 

 into the general convexity of the shell. Post-umbonal slope sub- 

 angular and extending to the post-basal extremity. No cincture. 

 Cardinal slope concave. Surface marked by concentric lines of 

 growth that are plainly visible to the unaided eye, and by fine 

 radiating strife that give a beautiful cancellated structure to the 

 cast under an ordinary magnifier. This surface ornamentation is 

 doubtless plainly visible on the shell itself. 



This species will be readily distinguished by its general form, 

 obliquely truncated, posterior end, concave cardinal slope and 

 surface ornamentation. 



Found by R. A. Blair in the Chouteau limestone, near Sedalia, 

 Missouri, and now in the collection of S. A. Miller. 



MACRODON TETTISENRIS, D. Sp. 



Plate II, Fig. 17, right valve; Fig. 18, right valve of a larger 

 specimen, with the anterior end broken off. 



Species below medium size. Shell subelliptical or subovate, 

 wider behind. Length about one and two-thirds the height. 

 Cardinal line straight and almost equaling the greatest length of 

 the shell. Anterior end gently rounded into the basal margin. 

 Posterior end somewhat subtruncated in the upper part and 



