290 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



of concave (see fig. la, and compare with fig. db). I have not seen casts 

 of the interior; but, from the similarity of the shell to that of the last- 

 described species, there can be little doubt in regard to its muscular 

 impression being as in that form. 



The specific name was given in honor of the late Dr. B. F. Shumard, 

 of Saint Louis, who was one of our most able palaeontologists. 



Locality and position. — Same as last. 



A 11 ■ so in y on patelliformis, M. & H. 



Plate, 18, tigs. 5, ,i, b, c,/(uot <l ; and e ?). 



Hcleion patelliformis, Meek and Haydeu (1856), Proceed. Aead. Nat. Sci., VIII, 68. 

 Anisomyon patelliformis, Meek and Hayden (I860), Am. Jour. Sci. and Aits, XXVIII, 35, pi. 1. 



Shell thin, ovate or subelliptic-patelliform, usually broadest toward the 

 posterior or longer side; summit moderately elevated, a little compressed 

 laterally, located in advance of the middle, immediate apex having the generic 

 characters well defined ; lateral slopes nearly straight, converging to the apex 

 at an angle of about 90° ; anterior slope straight, a little convex or slightly 

 concave; posterior slope convex, and generally showing very faint traces of 

 a few radiating ridges; surface marked by line, \f\\ obscure lines of growth, 

 and indistinct indications of radiating stria?. 



Length, 0/14 inch ;. breadth, 0.83 inch ; height, 0.40 inch. 



Several internal casts of this species in the collections show very 

 distinctly the peculiar muscular impression characteristic of the genus. 

 Sometimes ils enlarged anterior extremity on the right side is left completely 

 disconnected, in consequence of the slender part passing around behind being 

 separated into a row of small spots, or entirely obsolete. 



In a few instances, I have observed the border on the right anterior 

 side in front of t lie muscular impression a little raised, as if slightly modified 

 by the protrusion there of the head or some other organ (see figs. 5 a, b); 

 but this may have been produced by accidental distortion or inequalities in 

 the surface upon which the animal had temporarily fixed itself. It is not 

 often that specimens are found with the small, recurved apex of the summit 

 unbroken; but I have seen it in a few instances, as shown in fig. 5, a. 

 Sometimes it has the appearance of being perforated, and in other specimens 

 it certainly comes to an imperforated point, as is probably always the case 

 when entire. 



