354 SYSTEMATIC PALEONTOLOGY 



with small, shallow concentric grooves near the beak, slightly undulated 

 over the rest of the shell by obscure and irregular growth lines, or in 

 some specimens almost perfectly smooth over this outer part; teeth 

 robust; ligament areas impressed; pallial line distinct; margin smooth 

 or crenulated. 



This species is doubtless the ancestor of Astai-te thisphila from which 

 it may be readily separated by its much smoother surface, much flatter 

 form and thinner shell, as well as by its lacking the flattening or depres- 

 sion near the umbo so characteristic of thisphila. It has a less promi- 

 nent beak, is flatter, less symmetrically rounded, thinner and much less 

 smooth on the surface than Astarie ohruta. It is found only at a lower 

 horizon than either of the other two species mentioned above. 



Length, 25 mm.; height, 21 mm.; diameter, 4 mm. 



Occurrence. — Calvert Formation. Plum Point, Church Hill, Reed's. 



CoZZecitons.— Maryland Geological Survey, Johns Hopkins University. 



AsTARTE OBRUTA Conrad. 

 Plate XCIV, Figs. 5, 6. 



Astarte obruia Conrad, 1834, Jour. Acad. Nat. Sci. Phila., vol. vii, 1st ser., p. 150. 

 Astarte ohruta Conrad, 1840, Fossils of the Medial Tertiary, j). 43, pi. xxi, fig. 2. 

 Astarte obruta Conrad, I860, Proc. Acad. Nat. Sci. Phila., vol. xiv, p. 578. 

 Astarte obruta Meek, 18(j4, Miocene Check List, Smith. Misc. Coll. (183), p. 7. 

 Astarte (Ashtarotha) obruta Dall, 1903, Trans. Wagner Free Inst. Sci., vol. iii, pt. vi, 

 p. 1490 (in part). 



Description. — " Shell triangular, convex, smooth, with a few obsolete 

 undulations; beaks prominent, sulcated, margin crenulated. . . . 



"Allied to A. undulata Say, but is more convex and not profoundly 

 undulated; the umbo is not flattened." Conrad, 1834. 



Shell nearly equilateral, moderately thick; the sulcations on the beak 

 usually not prominent and extending but a very short distance from the 

 tip of the beak; the rest of the gently convex surface smooth except for 

 a few broad, almost obsolete, undulations; surface occasionally crossed 

 from beak to base by exceedingly faint, slightly impressed, radial lines; 

 beak projecting, acute, with its very tip curved somewhat forward. 



The gently rounded outline, and moderately convex, almost smooth 

 surface serve to distinguish this species from any other. It is charac- 

 teristic of the horizon of the upper fossiliferous bed at Governor Run, 

 having been found, so far, at no other horizon. 



