USE OF THE TABLES. 



279 



shell is an Ostrea. The next class (the Univalves) may 

 be treated in the same way. A whelk, a shell common 

 on our coasts, belongs to this class. The second table 

 must be consulted. There are five orders, which must 

 each be examined. The shell in question cannot be of 

 the Order Pteropoda, because it is neither cartilaginous 

 nor horny. It cannot belong to Gasteropoda, because it 

 is not cup-shaped nor slightly rolled up. It may belong 

 to Trachelipoda, because it is spiral. In the first division 

 of that order the aperture is entire, which that of the 

 whelk is not. The second division has the aperture with 

 a canal or notch : this agrees with the specimen in hand. 

 Each family of that division must now be examined. It 

 cannot belong to Canaliferidae, because it has not a canal, 

 nor the right lip thickened. The Pteridse have the right 

 lip greatly dilated or lobed : that family may therefore be 

 passed over. The Purpuridae have a short canal turned 

 back, or a notch, and the form of the shell is globular. 

 The whelk is notched, and its form is rather round ; and 

 as it could not belong to the other two remaining fami- 

 lies, we may suppose it is one of the Purpuridae. The 

 genus is next found by consulting the account of that 

 family in the work, and it will be with ease ascertained 

 that the whelk is a Buccinum, By affixing a number to 

 the specimen, corresponding to that in the book, it may 

 be referred to at any time to refresh the memory. 



The Annulata and Cirrhipeda have not been included 

 in the tables, as their names are more easily ascertained 

 than those of the other classes, from there being few 

 genera, and their general form and appearance being very 

 different. 



