2 MOLLUSCA. 



at the sides of the neck they are called Pteropoda ; when 

 they crawl on the helly by means of a muscvilar foot 

 they are termed Gasteropoda ; those furnished with a pair 

 of ciliated arms arising from the mouth constitute the 

 Brachiopoda ; those without a head and having the mantle 

 protected by two shelly valves are named ConcMfera, while 

 those without any shell and covered merely with a fleshy 

 mantle comprise the Tunicata. 



The following is a Synopsis of the Classes : — 



I. Cephalopoda or Cephalopods. 



Animal with the foot wanting or rudimentary. 

 Head large, distinct, furnished with eight, ten, 

 or more arms, by means of which they crawl 

 head downwards. 

 II. Pteropoda or Pteropods. 



Animal with the foot wanting or rudimentary. 

 Head prominent, with one or two pairs of fins 

 on the side of the neck, by which they move 

 about in the ocean. Body often covered with 

 a thin glassy shell. 



III. Gasteropoda or Gasteropods. 



Animal crawling on a foot placed under the body. 

 Head distinct, furnished with eyes and tentacles. 

 Body usually protected by a conical or spiral shell. 



IV. Concliifera or Bivalves. 



Animal with a foot placed under the body. Head 

 indistinct. Mouth placed between the gills. Body 

 enclosed between two equal or subequal valves 

 united along the back by a cartilage. 

 V. Brachiopoda or Brachiopods. 



Animal destitute of a foot. Mouth placed at 

 the base of two spirally-twisted ciliated arms 



