REPORT ON ZOOLOGY. 217. 



different from those generally adopted. Blainville's primary 

 subdivision of his type Malacozoaires is into three classes, esta- 

 blished upon the characters of the head. In the first class, Ce- 

 phalophores, which answers to the Cephalopoda of Cuvier, the 

 head is well distinguished from the body. In the second, Para- 

 c4phalophores, it is less strongly marked. In the third, Ac4- 

 phalophores, it can be no longer observed. The Parac4phalo- 

 phores include the Gasteropoda and Pteropoda of Cuvier, though 

 arranged upon a very different plan, the characters of the sub- 

 ordinate groups being derived in the first instance from the re- 

 productive organs, and afterwards from the respiratory or- 

 gans. Thus we have the three subclasses oiParac^ph. Dioiques, 

 P.Monoiques, and P. Hermaphrodites, each of which is divided 

 into two or more orders, according to the structure of the bran- 

 chiae. The third class, Acephalophores, is divided immediately 

 into four orders, which are likewise characterized from the re- 

 spiratory organs. The first of these orders, Palliohranches, 

 answers to the Brachiopoda of Cuvier ; the second, Rudistes, 

 comprises the Lamarckian family of bivalve Mollusca bearing 

 the same name ; the third, Lamellihranches^ includes the great 

 bulk of Cuvier's Testaceous Acephala ; and the fourth, Het4ro^ 

 branches, his Naked Acephala. Blaiuville does not include 

 either the Cirripeda or the Chitones amongst his true Malaco- 

 zoaires, but regards them as forming a subtype, Malentozoaires, 

 leading directly off to the Articulate Animals. In this group 

 they constitute the two orders of N4tnatopodes and Polyplaxi- 

 phores respectively. 



The latest systematic work in this department with which 

 I am acquainted, is the excellent little Manuel des Mollusques * 

 by M. Rang, published in 1829. This gentleman is also the 

 author of a valuable monograph on the genus Apli/siaf, as well 

 as of some other important memoirs relating to the Mollusca. 

 His arrangement of these animals is nearly the same as that of 

 the R^gne Animal. At the same time there are some alterations 

 with respect to the primary divisions. Thus, he sinks the class 

 Brachiopoda, regarding that group as only an order among the 

 Acephala, in which last class he admits as another additional 

 order the Rudistes of Blainville. He has also adopted some 

 new orders in the class Gasteropoda. Some of his families and 

 other subordinate divisions he has borrowed from Lamarck and 

 Ferussac. This work contains many new and original observa- 

 tions. 



The arrangement of the Mollusca in the second edition of the 



• Manuel de VHistoire Naturelle des Mollusques et de leurs CoquUles, ^c. 

 Paris, 1829. f Hisloire Naturelle des Aplysies. Paris, 1829, fol. 



