100 MIOCENE FAUNA. 



lensis, Lam., P. cypris, D'Orb., P. palmatus, Lam., P. pusio, 

 Linn., sp., P. scabrellus, Linn., and P. solarium, Lam.) are abun- 

 dant. Eleven species are extinct ; but three are still to be met 

 with in European seas. 



The pearl-mussels (Aviculacea) and the Mytilidse are much 

 less numerous, the former being represented only by a few spe- 

 cies of Avicula, Perna, and Pinna, and the latter by four species 

 of thin-shelled Modiolce, which probably lived at great depths. 



The Dimyaria are far richer in species than the Monomyaria. 

 They are divided, in accordance with the structure of their mouth, 

 into two great groups, namely : the 



Integropallealia, in which the impression of the mantle is 



entire ; and the 

 Sinupalledlia, with a sinus or bend in the impression. 



Of the former, nine families were represented in the Molassic 

 sea. Of the Arcacea there are four species of the nearly circular 

 Pectunculi, two of which (P. insubricus and pilosus) are abundant, 

 and nine species of Area, with regular boat-shaped shells. One 

 of these (Area nivea] appears as early as the Upper Eocene, and 

 is still found living in the Red Sea; two other species (A. lactea, 

 Linn., and A. barb at a, Linn.) have also survived to the present 

 day. The Cardita, distinguished by their thick shells traversed 

 by strong longitudinal ribs, are also among those Mollusca which 

 made their appearance very early in the history of the earth; and 

 eleven species still peopled the Molassic sea, of which one (Car- 

 dita caliculata, Linn.) is now met with in Europe and near Sene- 

 gambia, whilst another species (C. antiquata, Linn.) is confined 

 to the Mediterranean, and the remaining nine became extinct 

 during the Miocene epoch. 



The family Lucinida furnishes the genera Diplodonta and 

 Lucina, the former with two still-living species, the latter with 

 twelve species ; the Nuculida are represented by the genera 

 Nucula and Leda, with eight species; the Chamacea by two 

 extinct forms of the now tropical genus Chama ; and the Cardi- 

 acea by the genera Cyprina, Isocardia, and Cardium, the last- 

 mentioned being among the most abundant bivalves in brackish- 

 water deposits. The Molasse possesses eighteen species, gene- 

 rally with large convex shells traversed by strong longitudinal 



