t 



5l4 DESCRIPTION OF THE MUSEUM, 



shell. In the Jissurellce there exists no partition, 

 but the apex is pierced. 



To the family of the phjllidice belong the genus 

 umbrella, vulgarly called Chinese parasol, a very 

 rare shell of which we have four beautiful spe- 

 cimens ; the patella of which we have seventy- 

 five species and more than three hundred spe- 

 cimens, mostly exotics ; the chiton, whose shell 

 is formed of several small pieces so adapted as to 

 admit of the animal's rolling itself into a ball in 

 the manner of the woodlouse ; we have twenty- 

 five species. 



The last order of univalve mollusca (ptero- 

 poda) is divided into five genera. We shall only 

 mention the hyalcea and the clio : we have seven 

 species of the first ; the most common is the tri- 

 dentata {anomia tridentata, Forsk.) which is seen 

 in great quantities swimming on the surface of 

 the water between the tropics. The clio borealis 

 is so abundant in the North seas, that it forms 

 the principal food of the whales and other large 

 cetaceae. 



Here ends the series of univalve: we shall 

 now examine those whose shelly consists of 

 two pieces, and which are named conchifera. 



The first family, the tubicola, comprehends the 

 genera aspergillum, fistulana and teredo. The 

 two first come from the Moluccas, and are very 



