GASTEROPODA OF THE UNITED STATES. 9 



uniformly developed throughout, but is thickest upon the 

 pedal disc, the tail, and the upper surface of the mantle, 

 and thinnest upon the head, tentaculae, and reflected 

 border of the mantle. 



Figure B. 



In the testaceous genera, upon the part of the body 

 corresponding to the interior of the shell, it appears as if 

 the mucous layer had been pushed downwards to form 

 the collar (fig. C, 1*) ; but it may be still traced over the 

 surface of the turbinated portion, as a delicate, tessel- 

 lated epithelium. 



Figure C. 



The mucous glands are very numerous in the mucous 



Fig. B, disposition of the tegumenta in Tebennophorus. 1. mucous 

 •lamina; 2, muscular lamina; 3. peritoneum ; 4. visceral cavity; 5. pulmo- 

 nary chamber ; 6. interval between the two muscular layers. 



Fig. C, disposition of the tegumenta in Helix, Bulimus, &c. Tlae refer- 

 ences are the same as in figs. A and B, except 1*, w^hich is the collar. 



