CASSIDARIA. 



The general form of the shells of this Genus is oval 

 DV oblong, and they are most commonly ventricose, the 

 last volution being large and by far exceeding the others 

 in size; the spire is short, and the aperture longitudinal, 

 rather elongated and terminating at the base in a recurved 

 canal, turning upwards when the shell is laid on its 

 aperture. Oute7^ lip thickened, reflected, often dentated 

 within; i?mer lip expanded, covering the lower part of 

 the last volution and columella, but standing free from 

 it at the base just above the canal. A thin horny epider- 

 mis covers the outside of the shells when living, and in 

 good condition ; but this seldom remains when they come 

 into the market. Its operculum we have never seen, 

 though we have no reason to donbt its having one^ and 

 that it is thick and horny. 



The recent species of this Genus are not numerous, 

 they are mostly grooved and tuberculated on the outside; 

 Lamarck mentions that the expanded inner lip is gene- 

 rally tuberculated, granular or rough, but we have omit- 

 ted this in our definition of the Genus, because it is not 

 actually true of several of the more common species, and 

 because there is, as we have before mentioned, some rea- 

 son to doubt the propriety of retaining his C. Oniscus, 

 which shows this character most strongly, among the 

 Cassidaria?, Of fossil species there are very few, they oc- 

 cur in the tertiary beds ; one very elegant species, the 

 C. carinata, is common in the Calcaire grossier near Paris; 

 it is also found in the lyondon clay, and the contempora- 

 neous stratum of Piacenza. 



Fig. 1. Cassidaria, echinophora. 



2. Tyrrhcnuigfi. 



3. cari7\ata. 



