36 Trans. Acad. Set. of St. Louis. 



marked by sharply defined concentric ridges, with less dis- 

 tinct radiating striae which become nodose at their intersec- 

 tions with the concentric ridges. The posterior slope from 

 the umbonal ridge smooth, except for rather faint lines of 

 growth . 



Bemarks. The specimen upon which this species was 

 founded by Hall is a very imperfect one from the " Yellow 

 Sandstone " of Burlington, Iowa, in which only that portion 

 of the shell anterior to the beak is preserved. The illustra- 

 tion of the type specimen shows the shell with a somewhat 

 more sharply pointed anterior end than is possessed by any of 

 the Northview specimens, but the surface markings in the two 

 are peculiar and are apparently identical, so that it is believed 

 that they belong to the same species. The species may be 

 easily distinguished from the last by its smaller size, its more 

 posteriorly placed beaks, and by its peculiar surface mark- 

 ings. The surface markings and the size will also distinguish 

 it from any of the other species of the genus. 



Fragments of this species are not uncommon at Northview, 

 but only one specimen approaching perfection has been found. 



SaNGDINOLITES WEBSTERENSIS n. Sp. 



PL III. f. 7. 



Shell 75 mm. in length, more than twice as long as broad, 

 subelliptical in outline, narrower in front. Anterior end nar- 

 rowly rounded; posterior end broadly and quite regularly 

 rounded ; basal margin nearly straight posteriorly but rounded 

 upward at the anterior extremity. Hinge-line more that two- 

 thirds the length of the shell, straight posterior to the beak 

 and sloping forward anteriorly from the beak. Valves mod- 

 erately convex, the beaks situated near the anterior end. 

 An obscurely angular, inconspicuous, umbonal ridge extends 

 from the beak to the posterior basal margin of the shell, and 

 upon the cardinal slope above this umbonal ridge three addi- 

 tional inconspicuous ridges may be detected. The surface 

 of the shell ornamented with irregular concentric lines of 

 growth. 



Remarks. This species closely resembles a shell from the 

 Waverly Group of Licking County, Ohio, which was identi- 



