1880.J NATURAL SCIENCES OF PHILADELPHIA. 33 



Weinheim (Sandherger,^^ Conchylien des Maimer Tertiarheckens,'''' 

 p. 367). 



Mytilus incurva, Conr. 



This large species of Mytilus may perhaps be taken as the rep- 

 resentative of M. Haidingeri^ Homes Q'-Fossilen 3IoUusken des 

 Tertidrheckens von Wie7i,^^ Abhand. d. k. k. geolog. Reichaanntalt^ 

 iv, p. 356), found both in the Oligocene (Eggenbnrg) and Miocene 

 divisions of the Vienna basin. Rolle (Sifzungsberichte d. k. Akad. 

 d. Wissenschaften, 1859, p. 64) and Sandberger consider the M. 

 Tlaidingeri as the eqnivalent of M. Faujasi, Brongn., occurring at 

 numerous Olia-ocene localities of the Vienna and Mentz basins. 



Isooordia Markoei, Conr. 



Tliis Isocardia is, it appears to me, erroneously referred by 

 HVrnes {loc. cit., p. 165) to the /. cor. L., from which it is very 

 readily distinguished by its relatively much greater height, and 

 greater development of the umbones. It is a singular fact, that 

 this species of Isocardia was followed in the later period by the 

 T. fraterna,'^ Say, which is barel}' distinguishable from fossil 

 examples of the I. cor from Astigiana and Sicil}'. 



It is worthy of remark, that Rolle (loc. cit., p. 81), as early 

 as 1859, only four years after Bey rich first applied the term Oligo- 

 cene to some of the middle Tertiary deposits of northern Germany, 

 hinted at the possible existence of the same formation on the 

 banks of the Patuxent, his conclusions being drawn from an 

 examination, among other fossils, of specimens of Lucina anodonta, 

 Say, Area idonea^ Conr., and Cardium laqueatum^ Conr. 



* On comparison with si)ecimens from the English Crag this species will 

 be found to differ very broadly from the /, {Cyprina^ rustica of Sowerby, 

 with which it has been confounded, 



