5l2 DESCRIPTION OF THE MUSEUM. 



of the rarest and most esteemed shells ; we have 

 two specimens of it three inches long. The 

 only known species of the genus vermetus was 

 brought from Senegal by Adanson. 



8th. The four genera which compose the fa- 

 mily macrostoma are not very numerous ; that of 

 the haliotideae consists of seventeen species, all 

 very beautiful, amongst which the h. iris is un- 

 doubtedly the most brilliant of shells. 



gth. The genera natica, nerita, neriiina, navi- 

 cella, and janikina, belong to the family of the 

 nerilacea: each of the three first comprehends 

 more than thirty species. The neritinae and the 

 navicellae are found in rivers ; the last are from 

 isles of France and Bourbon. We have three 

 species of janthina of a lilac colour. The animals 

 belonging to this genus have a cellular bladder, 

 which they draw into their shell or extend be- 

 yond it, as they wish to remain under the water 

 or to float upon its surface. We have a speci- 

 men preserved in spirits. 



loth, nth, and i2th. The families of the pe- 

 ristomatce, the melanice, and the tymncece, com- 

 prehend nine genera which inhabit fresh waters. 

 The rarest species is the cerithiumfluviatile, Lin., 

 from Madagascar. We have twenty-seven spe- 

 cies of the planorbis and twenty-five of the 

 lymnaeae. These shells are interesting, because 



