216 BERMUDA. 



The animals of this genus differ from all other 

 Brachynra, in having the abdomen extended; and 

 from the Other Notopoda, in having the six inter- 

 mediate legs terminated bj oval plates or fins. 

 Shell, wedge-shapedj or oblong ; truncated anteriorly. 

 The typical species most common around our shores 

 is the Ranina serrata. 



MoLLUSCA (or Shells). — The mollusea, or shells 

 and shell-fish, as they are usually called, although 

 several have no shells or calcareous coverings, pre- 

 sent many objects of interest to the naturalist, and 

 are not unimportant in their various uses to man. 



As the great vertebrate division includes the four 

 distinct classes of beasts, birds, reptiles, and fishes, 

 so does the great division of moUusca contain six 

 classes, distinguished by characters vyhich I shall 

 presently enumerate. 



It has been observed, as a distinction between the 

 vertebral and the invertebral animals, that v^hile in 

 the former the bones or hard parts are more or less 

 formed of phosphate of lime, the hard parts of the 

 latter, such as the shells of the moUusca and Crus- 

 tacea, and the stony matter of corals and madre- 

 pores, are chiefly composed of carbonate of lime. 



The Mollusca present every kind of mastication 

 and deglutition ; their stomachs are sometimes simple, 



