MIOCENE MOLLUSCA AND CKUSTACEA. 67 



SINUPALLIA. 



Family VENERIDiE. 



Genus V^ENUS Linnreus. 



Venus Ducateli. 



Plate xi, figs. 1-7. 



Venus Ducateli, Conrad : Miocene Foss., p. 8, PI. iv, fig. 2 ; Proc. Acad. Nat. Sci., 

 1862, p. 574; Meek Check List, p. 9; Heilprin, Tert. Geol. U. S., p. 85 Acad. 

 Nat. ScL, Phil., 1887, pp. 397 and 403. 



"Shell suborbicular, convex, thick; disk with numerous approximate, 

 recurved ribs, laminar and much elevated towards the posterior margin; 

 extremity obtuse; beaks distant from the anterior margin; umbo not inflated; 

 lunule defined by an impressed line, not very profound; posterior margin 

 rectilinear; two of the cardinal teeth in the left valve remote, thick, bifid; 

 anterior tooth much compressed." (Conrad.) 



Mr. Conrad's type specimens, a very imperfect right valve and two 

 fragments, are before me. I have also several other valves, and one pair 

 of valves, which appear to me to belong to the same species, but they 

 differ mostly in the outline form and in the character of the surface. 

 This latter feature, however, is one on which no reliance can be placed, 

 as the true surface characters have been denuded or removed by the 

 action of weather or by corrosion. The surface in their present condition 

 is very rugose, being marked by heavy elevated ridges which are left 

 standing separate, by the removal of the adjoining ribs, or of intermediate 

 portions of the outer layers of the shell; still they do not show evidences 

 of having ever possessed the structure now seen on Mr Conrad's speci- 

 mens. Yet I have no doubt they originally possessed it to a greater or 

 less extent. They present very close resemblances to Venus mercenaria 

 in many respects, but are thicker on the margin, rather more ventricose, 

 shorter posteriorly, and lack the slight flattening between the middle of 

 the valves and the posterior umbonal ridge which so generally marks 

 specimens of that species. In the interior the anterior cardinal tooth of 

 the left valve is generally bifid as well as the other, which in V. mercenaria 

 is not the case, and the posterior tooth is placed at a different angle, being 



