INVERTEBRATES. 157 



of our specimens, we have been able to see traces of the impressions of these 

 teeth, the presence of which establishes, we think, the correctness of our sug- 

 gestion that it does not properly belong to the genus Cardiomorplia. 



It *s not improbable that some of the species rarjged by Prof. deKoninckinhis 

 genus — when all their characters can be made out — may be found congeneric 

 with our shell ; though it is manifest those he considered the typical species 

 are not, since he distinctly states that the hinge is without teeth, and provided 

 with a smooth lamina from the beaks to the posterior extremity, as some of his 

 figures show. In addition to this, all the species described by him, (with one 

 single exception, which is a transverse shell, and apparently a wide departure 

 from his typical species, as well as from ours,) are merely marked by concentric 

 striae, and show no traces of the regular radiating costse seen on our shell. 



Cardiopsis radiata, M. and W. 



PI. 14, Figs. 6a, 65. 



Cardiomorpha radiata, Meek and Wortiien, Oct., 1860. Proceedings Acad. Nat. Sci., 

 Philad., p. 448. (Not G. radiata, deKoninck, 1844. An. Foss., p. 109.) 



Mcgarnbonia Lyoni, Hall, Dec, 1860. Report Regents University, New York, p. 110. 



Shell sub-circular, gibbous in the central and umbonal re- 

 gions, a little higher than wide, slightly oblique ; basal border 

 more narrowly rounded than the front and anal margins; hinge 

 border short, apparently a little arched ; beaks gibbous, rising 

 somewhat above the hinge, abruptly pointed, incurved, and 

 showing a tendency to curve forward at the immediate points ; 

 surface ornamented by numerous fine, regular, rather rounded 

 radiating strise, some seven or eight of which may be counted 

 in the space of 0.20 inch, at the middle of the base. Height, 

 about 1.05 inch ; length, 0.95 inch ; breadth or convexity, near 

 0.76 inch. 



This species is more like Cardiomorplia ovata, Hall, (Iowa Report, p. 522, pi . 

 7, fig. 10*), from the same„horizon (now made the type of a new genus Dexio- 

 bia, by Prof. Wmchell), than any other shell' with which we are acquainted, 

 but is more nearly circular in form, has more depressed beaks, and much coarser 

 and more distinct strias, while its umbonal slopes are less prominent. 



* Not O. ovata, d'Orbigny. 



