187 



The marginal outline of this specimen would seem to be suiEciently 

 different from that of the R. com2wes8a and R. convexa of Ulrich, as 

 figured on plate 56 of the seventh volume of the Report of the Geological 

 Survey of Ohio, to justify its separation from either, as a distinct species. 

 Thus, in R. compressa the anterior side is proportionately longer and 

 more broadly rounded than that of R. recta, and the posterior end of 

 the former is less pointed below. In R. convexa the anterior side is also 

 much longer than that of R. recta, the cardinal margin of the former is 

 more arched and its posterior end is represented as more produced below. 



CoNOCARDiDM ANTIQUUM, D. Dale Owen. (Sp.) 



PI eurorhvnchus antiqua, Owen 1852. Geol. Rep. Wiscons. , Iowa and ^linn., 



Table 2b, iig. 19. 

 Conocardium antiquum, S. A. Miller. . . , 1883. Amer. Pal. Foss., second edit., p. 310. 



1889. N. Amer. Geol. and Palseont., p. 472. 



Lower Fort Garry, Owen, 1848. "This small and delicately formed 

 Pleurorhynchus is, I believe, the first of the genus that has been discov- 

 ered in this country in rocks of Lower Silurian age.'' Owen. Only one 

 specimen would seem to have been obtained, which is badly figured, and 

 the species has never been described. 



EdMONDIA (?) VETUSTA. (ISl. Sp.) 

 Plate 20, fii?. 8. 



Shell small, moderately convex, obliquely subovate, a little longer than 

 high and very inequilateral. Anterior side short, its margin abruptly 

 contracted both above and below and narrowly rounded or narrowly sub- 

 truncated at the end : posterior side longer and broader (in the direction 

 of its height) than the anterior : posterior end obliquely subtruncate and 

 somewhat contracted above, rather narrowly rounded and moderately 

 produced below : ventral margin broadly rounded, but more convex pos- 

 teriorly than anteriorly, most prominent behind the midlength and 

 straighter in front : cardinal margin, behind the beaks, very short, faintly 

 convex and slightly ascending : beaks moderately prominent, incurved 

 and placed consit'erably in advance of the midlength. 



Surface marked by concentric lines of growth, and on some specimens, 

 when viewed with a lens, there are obscure indications of close set, 

 minute radiating stria;. Hinge dentition not known with any degree of 

 certainty, but probably edentulous. On each side of the umbones there 

 is a long and narrow, widely divergent slit or groove, at a short distance 

 from the cardinal border and not far from parallel with it. IMusoular 

 impressions not distinctly defined, though the scar of the anterior adductor 

 seems to have been vertically elongated. 



