246 NEW YORK STATE MUSEUM 



and much the longer pair containing the eyes, the lower and 

 shorter pair, the olfactory nerves. The mouth is situated at the 

 anterior basal part of the head. Immediately below it is the 

 opening into the pedal gland. The anterior upper part of the 

 body is rounded; the posterior part is more acute. 



The dorsal part of the animal is produced in a spirally coiled 

 mass, containing the whole of the digestive gland, and parts of 

 the alimentary, circulatory and reproductive organs, and is there- 

 fore known as the visceral mass. 



The integument of the foot consists of a thick mucous-secret- 

 ing membrane, with a muscular substratum. There are numer- 

 ous mucous glands occupying nearly the whole of the membrane. 

 The muscular substratum consists of unstriped fibers, arranged 

 longitudinally, transversely and obliquely. Interior to this in- 

 vestment of the foot is a muscular membrane inclosing the di- 

 gestive and reproductive organs, which is sometimes called the 

 peritoneum. 



The dorsal part of the animal is inclosed in the shell and is 

 an exact mold of the shell. The integument of this part is very 

 thin and semi-transparent and is known as the mantle. Where 

 the visceral sac joins the foot the mantle is very much thickened, 

 forming a muscular collar, which is the shell-building organ of 

 the animal. 



When the animal is at rest or alarmed, the foot is contracted 

 entirely within the shell, occupying the space at other times 

 filled by the pulmonary cavity. The pulmonary chamber is very 

 large and is situated in the outer part of the lower whorl. When 

 the foot is protruded, the pulmonary rete still remains in contact 

 with the shell, thus leaving a large cavity. It is into the space 

 obtained by the collapse of this cavity, when emptied of air, that 

 the animal withdraws when contracted. Thus the pulmonary 

 chamber of testaceous snails is as much larger than the chamber 

 of the naked slugs, as the volume of the foot superadded. 



