CRASSATELLA 



side of the umbo, rather elongated and not: so distinct 

 as the other on the posterior side. There are two, 

 distant J lateral, rather oblong*, muscular impressions. La- 

 teral teeth none, or nearly obsolete. The shells of this 

 Genus are generally very thick, particularly the more aged 

 specimens ; the recent ones have a brownish, somewhat 

 horny epidermis ; all are, more or less, transversely grooved, 

 particularly near the umbo. 



The few recent species of this Genus at present known, 

 are marine ; several of them are brought from the coasts of 

 New Holland; we have represented two, the C. Kingicola 

 and C. rosirata. The C. iumida and C, compressa are 

 fossil species from the Calcaire grossiere of the environs of 

 Paris ; we have another fossil species, the C. sulcata^ very 

 common at Hordwell; it appears to be characteristic of the 

 London Clay. 



Fig. 1 Insides of Craasatella tnmida. 



2 Crassatella compressa. 



3 Crassatella rostrata 



In a second plate are three views of Crassatella Kingicola, 



