COLLECTION OF SHELLS. 5l3 



when met with in the fossil state, they prove the 

 str ata to be of fresh water formation. 



1 3 th. The animals composing the numerous 

 family helicoidea are very noxious on cultivated 

 ground. The species most esteemed by concho- 

 logists belong to the genera bulimies, achatina, 

 and auricula. We have one hundred and ninety- 

 two species of helices ; these are terrestrial shells 

 from all countries, the most curious. of which 

 is the h. vesicalis. 



Our knowledge of the next order, gasteropoda, 

 is due to the anatomical labours of M. Cuvier, 

 and from his observations M. de Lamarck has di- 

 divided it into families. The greater number of 

 the animals which compose it are destitute of 

 a shell; we shall notice only those which are 

 provided with one. The limax and other genera 

 which have no shell are preserved in spirits of 

 wine among the naked mollusca. 



The family of the bullcece is very numerous , but 

 owing to the lightness and fragility of their shell, 

 they are rare in collections ; on this account that 

 of the Museum which has twenty-four species is 

 valuable to the student. 



The family caljpirece is composed of eight ge- 

 nera: the crepidulce to the number of fourteen 

 species, and the calyptrcece to that of twenty, are 

 distinguished by the interior partition of their 



33 



