PULMOGASTROPODA. 8 1 5 



Family 3. Siphonariid.e. — This family comprises certain marine 

 Gastropods, of amphibious habits, which agree with the normal 

 Pulmonates in the possession of a pulmonary chamber. The shell 

 is limpet-shaped, unsymmetrical, and usually radially ribbed. The 

 muscular impression in the interior of the shell is interrupted by a 

 lateral sinus corresponding with the opening of the pulmonary sac. 

 The type-genus of this family is Siphonaria itself, the living species 

 of which are found in tropical seas. The earliest fossil forms appear 

 in the Eocene deposits, but the shell is with difficulty distinguished 

 from that of the Patellidce. 



Family 4. Gadiniid.e. — This family comprises marine Pulmo- 

 nates, which possess a patelliform shell, and differ from the preced- 

 ing family only as regards the armature of the mouth. No undoubted 

 fossil forms of the family are known, but Professor von Zittel is 

 disposed to refer here the genus Vale?iciennesia, in which the shell 

 is like that of a large limpet, but the apex is much incurved, and 

 an internal sulcus and corresponding superficial fold extend from 

 the apex to the right margin, and exist in a less developed form on 

 the left side. This remarkable genus occurs in abundance in the 

 brackish - water Upper Miocene deposits (" Congeria - beds ") of 

 south-eastern Europe. 



