204 
INTRODUCTION. 
uniformly developed throughout, but is thickest upon the 
pedal disc, the tail, and the upper surface of the mantle, 
and thinnest upon the head, tentacular, and reflected 
border of the mantle. 
z 12 3 
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. 
FlGUKE C. 
The mucous glands are very numerous in the mucous 
Fig. B, disposition of the tegumcnla in Tebennophorus. 1. mucous 
lamina; 2. muscular lamina; 3 peritoneum ; 4. visceral cavity; 5. pulmo- 
nary chamber; C. interval between the two muscular layers. 
Fig. C, disposition of the teguments in Helix, Bttlimus, &c. The refer- 
ences are the same as in liy s. A and B, except I*, which is the collar. 
