OF CONCHOLOGY. 11 



Agassiz, who was unacquainted with the hinge character and in 

 doubt of its stratigraphical position. 



Tiiere seems to be no doubt that fresh water testacea existed 

 as early as the Carboniferous era, shells resembling Unionidae 

 occurring with univalves closely resembling the genera Limncea 

 and PJiysa. M'Coy has constructed the genus Carhonicola for 

 the Carboniferous Unios of Sowerby, and the present genus 

 bears a similar relation to the recent genus Margaritana, being 

 without lateral teeth. This family is found in the Wealden, but 

 the generic characters of the specimens seem to be undetermined. 

 The cast figured by d'Orbigny as a Cretaceous Unio is too ob- 

 scure to rely upon, but the Eocene Unio Edivardsi has unmis- 

 takably the hinge character of recent Unionidae, either belong- 

 ing to Unio or to a genus very closely allied to it. Meek and 

 Hayden have also described a few Eocene Uiiionidoi, of the 

 Western Territories. In the Miocene period, for the first time 

 in Palosontological annals, the family group of the Unio type was 

 diversified by various species of great variety of form and sculp- 

 ture similar to those now existing in the Mississippi and its tribu- 

 taries. This fresh water group existed in the Miocene of Europe, 

 whilst in the extended North American Miocene of the Atlantic 

 slope we have not yet found a single specimen of Unionidae. 

 This is remarkable, for where we find a species of Vivipani, a 

 Rangia and Cyrena^ we would expect to find an occasional ex- 

 ample of the Unionidae. 



In the Eocene of the I^aris basin Deshayes finds two species 

 of Anodonta and three of Umo^ two species of which latter 

 genus bear a general resemblance exteriorly to species of the 

 tributaries of the Mississippi, but they are very distinct as species 

 from any existing shells. The similarity of the Unionidae of the 

 European Miocene to the existing group of the United States is 

 accounted for from the fact that the fauna of that period is repre- 

 sented by the existing fauna of North America. 



CRASSATELLID^. 



PAL^OCARDITA, Conrad. 



Type Cardita Austriaca. 



I have stated in a former number of this Journal my belief 

 that the genus Venericardia, Lam., originated in the Eocene 

 period. The same may be said of Cardita, Brug. Stoppani 

 has described and figured a number of shells which he refers to 

 Cardita^ found in a bed which he terms infralias. The first of 

 these, 0. aspera, has more the habit of a Cardiiim than Cardita, 

 but as the hinge is neither figured or described, its generic char- 

 acters remain uncertain. The next species, C. Austriaca, appears 



