MIOCENE MOLLUSCA AND GKUSTACEA. 67 



SINUPALLIA. 

 Family VENERID^E. 



Genus VENUS Linnreiis. 



Venus Ducateli. 



Plate XI, figs. 1-7. 



Venus Ducnfeli, Com- Ml: Miocene Foss., p. 8, PI. iv, flg. '2; Proc. Acad. Nat. Sci., 



18(W, p. .574; Meek Check List, p. 9; Heilprin, Teit. (xeol. U. S., p. 8; Acad. 



Nat. Sci., Phil., 1887, i)p. 3!)7 and 403. 



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

 recurved rilis, laminar and iimcli elevated towards the jxisterior margin; 

 extrenaity obtuse; beaks distant from the anterior maro-in; uml)o not inflated; 

 lunule defined by an impressed line, not very profound; posterior marg-in 

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

 antei'ior tooth nuicli compressed." (Conrad.) 



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

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

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

 difter mostly m 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, t>r of intermediate 

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

 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 

 spt^cimens 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 



