CHAP. I. SYSTEM OF LAMARCK. 23 



(20.) To his second great division, Lamarck restricts 

 the title ofMollusca : these he again subdivides into the 

 five following orders : 1 . The Pteropoda, which forms 

 a part of our Cephalopoda. 2. The Hydrobranchia, 

 which includes the Nudibranchia, Scutibranchia, and 

 Tectibranchia of Cuvier ; together with the genera Ow- 

 chidium, Parmacella, Umax, Testacellus, and Vitrina : 

 these genera he places in his section Pneumobranchia, 

 and makes them the passage to his third order, or the 

 Trachelipodes, in which all the univalve shells are placed. 

 The fourth order is composed of the Cephalopoda, or 

 cuttlefish ; and the fifth contains the Heteropoda. 

 The genera belonging to each of these orders are as 

 follows : 



ORDER I. PTEROPODA. 



Hyalaea. Cleodora. Cymbulia. 



Clio. Limacina. Pneumodermon. 



c 4 



