A MONOGRAPH 



OF THE 



MOLLUSCA FROM THE EOCENE FORMATIONS 



OF ENGLAND. 



ORDER— PULMONATA. Cuvier. 



Pneumobranchtata, Lamarck. 

 Pulmobranchiata, Be Blainville. 

 Pulmonifera, Fleming. 



The Molluscs forming this order breathe the free air by means of a chamber 

 termed the pulmonary sac or cavity, placed beneath the dorsal surface of the anterior 

 part of the mantle, and communicating with the atmosphere by a lateral opening, 

 which can be dilated or contracted at the pleasure of the animal. The roof and walls 

 of this chamber are lined with a network of pulmonary vessels, by which the blood is 

 exposed to the air, and the renewal of this vital fluid is effected by movements of the 

 floor of the chamber, analogous with those of the diaphragm. 



The Pulmonated Molluscs are furnished with eyes, which are either placed at the 

 anterior extremities of two elongated cylindrical peduncles, or seated in the head of 

 the animal. Most of the genera in which the eyes are pedunculated, are also furnished 

 with shorter cylindrical tentacula, placed beneath the peduncles, but in some few 

 instances these appendages are wanting. In the genera in which the eyes are sessile, 

 the animal is furnished with two sub-cylindrical or compressed tentacles only. The 

 sessile eyes are variously placed ; in some genera they are seated at the inner sides of 

 the bases of the tentacles ; in others at the outer sides ; and in others on the frontal 

 disc. The peduncles and tentacles are both contractile, and in by far the greater 

 number of genera they are also retractile, that is, capable of being withdrawn under 

 the skin. They are eminently sensitive organs of touch. 



The head is well developed, and the mouth is provided with an apparatus 



•8 



