AND HABITS OF MARINE TESTACEOUS MOLLUSCA. 
513 
of feeding in the different land and fresh-water mollusca, will probably com¬ 
plete the general outline of this branch of zoology. Should leisure and oppor¬ 
tunity allow, I shall hope to pursue the investigation. 
I must not conclude without acknowledging my very great obligations to 
Mr. Dillwyn. His observations on fossil shells, published in the Philosophical 
Transactions, first suggested the inquiry; and the use of his valuable library, 
and still more, his own extensive information, have materially assisted me in 
the execution of it. 
Explanation of the Plate. 
Plate XIV. 
Trochus crassus. 
Fig. 1. The cartilaginous skeleton of the jaws. 
Fig. 2. Upper view of the jaws, with the tongue and its muscles. 
Fig. 3. Under view ; the ligament of the jaws divided to show the insertion 
of the retractor muscles of the tongue. 
Fig. 4. The stomach, laid open to display the contained oesophagus. 
a. The accessory cartilages. 
h. The muscles which expand the jaws. 
c. Portions of them which project the tongue. 
d. The transverse muscle which closes the jaws. 
e. The retractors of the tongue. 
f. A muscle passing from the tongue to the floor of the cavity. 
g. A small muscle which assists to expand the jaws. 
h. The lips of the stomach. 
i. The valve in front of them. 
