AMEKICAN JOUKNAL 



In regard to the family affinities of the group of shells here 

 under consideration, it is of course impossible to arrive at any 

 satisfactory conclusions, until specimens showing the hinge and 

 interior can be found. I have the impression, however, that 

 they belong either to the Anatinidce, or to some allied family. 



Sanguinolites (Promacrus) nasutus, Meek. PI. 1, fig. 1. 



Shell somewhat less than three times as long as high, rather 

 compress, especially in front of the keels, the greatest convexity 

 being about half way down these ridges ; basal outline forming a 

 long, very gently convex curve from end to end ; anterior side 

 long, compressed, cuneate, and narrowing regularly to the very 

 narrowly rounded extremity ; posterior side distinctly shorter 

 and wider than the anterior, with its truncated margin nearly 

 straight or but slightly convex in outline from its subangular 

 lower extremity obliquely forward and upward to the dorsal 

 margin, which is straight and slopes a little backward from the 

 beaks ; anterior dorsal margin forming a long, nearly straight 

 slope from the beaks to the anterior extremity ; beaks rather 

 depressed, compressed, and placed distinctly behind the middle ; 

 umbonal ridges well defined from* the beaks to the posterior 

 basal angle. Furrows and striae of growth moderately distinct ; 

 radiating striae of the umbonal region nearly obsolete. 



Length, 5*22 inches; height, 1*96 inches ; convexity of the two 

 valves about half way down the. keels, 0-97 inch. 



The typical and only specimen of this species I have ever seen 

 was given to me by Prof. Swallow in 1866. It was found at the 

 Choteau Springs in Cooper Co., Missouri, in what was called, in 

 the Geological Report of that State, the " Choteau limestone," 

 now known to belong to the oldest member of the Carboniferous 

 system, and to be equivalent to the Waverly series in Ohio, the 

 Marshall group of Michigan, and the Kinderhook group of Illi- 

 nois. 



Sanguinolites (Promacrus) Missouriensis, Swallow, MS. 

 PI. 1, fig. 2. 



Solen ? Missouriensis, Swallow, 1860. Trans. St. Louis Ac. 

 Sci. i., p. 655. 



Shell about four times as long as high, rather compressed ; 

 post-umbonal angular ridges well defined from the beaks to the 

 posterior basal extremity ; basal margin nearly straight from 

 end to end ; anterior side shorter than the other, but well pro- 

 duced, and narrowly rounded at the extremity ; posterior side 

 wider and near one-third longer than the other, with its trun- 



