KEY TO CLASSES OF MOLLUSCA 



A. Shell composed of two valves, or pieces, generally placed side 



by side. 

 Clams, Oysters Pelecypoda. 



B. Shell composed of eight separate pieces. 



Coat of Mail shells Amphincura. 



C. Shell composed of one piece, generally in the form of a spiral. 



Snails Gastropoda. 



D. Shell in the form of a hollow cylinder. 



Tooth shells .... Scapliopoda. 



E. Head with eight or ten arms, which are provided with numer- 



ous suckers ; shell generally absent. 

 Squid, Nautilus, Devil-fish Cephalopoda. 



"Each class," continued the Professor, "is divided into numerous 

 orders, and these in turn are divided into suborders, families, subfam- 

 ilies, and genera, and all of these divisions may be arranged in keys, 

 as you may see for yourself by consulting some of the books in my 

 library. I would advise each of you to procure a good manual of Con- 

 chology and study it carefully." 



Howard asked what was the most characteristic feature of shells, 

 which was not shared by any other branch of the animal kingdom. 



" The name Mollusca," answered Professor Parker, " is from the 

 Latin word Mollis, meaning soft, and is given to this class of animals 

 because their bodies are soft and fleshy. The most characteristic 

 features of the Mollusca are the creeping disk, or foot, and in all 

 but the Pdecypoda, the peculiar dental apparatus called the radula, 

 or odontophore. In geological history the Mollusca extend back almost 

 to the beginning of time, their remains being found in the early Cam- 

 brian rocks. There are at present about fifty thousand known living 

 species, and the same number of fossil species." 



As we were leaving to go to our several homes, the Professor handed 

 each of us a slip of paper, containing a list of some books on Conchology, 

 which he desired us to procure and study. 



Several days after this visit to Professor Parker's house, a concho- 

 logical club was formed, consisting of the quartette and several of their 

 young friends, who had become interested in the subject. Professor 

 Parker was by common consent elected an honorary member, and 

 was unanimously made the first president. A plan was outlined for 

 the winter, which embodied a thorough study of some of the most 

 interesting groups of the Mollusca. 



147 



