216 FOURTH REPORT — 1834. 



nearly the same as those of former authors. The Cirripeda, 

 however, are not included. The groups subordhiate to the classes 

 are established principally upon the organs of respiration. The 

 arrangement of the families and genera of the Gasteropoda is 

 grounded upon the form of the opercle, which leads in many 

 cases to very natural relations. Mr. Gray has the merit of 

 having studied this part more profoundly than any of his pre- 

 decessors. 



In 1824, M. Latreille published in the Ann. des Sci. Nat.* 

 a sketch of a new arrangement of the Mollusca, which was more 

 developed the following year in the Families Natiirelles. In this 

 last work, the primary division of these animals (from which the 

 .Naked Acephala and Cirripeda are entirely excluded,) is into 

 Phanerogama and Agama, the former including all those in 

 which copulation is necessary in order to reproduction, the latter 

 such as impregnate themselves. TYiq Phanerogama are further 

 divided into two large sections, the characters of which are de- 

 rived from the organs of motion. The first of these, which is 

 termed Pterygia, includes two classes, the Cephalopoda and 

 Pteropoda of Cuvier. The second, Apterygia, includes the 

 class Gasteropoda of the same author. In this last class, be- 

 fore arriving at the orders, which are characterized from the 

 organs of respiration, there is a subdivision according as the 

 sexes are separate, or united in the same individual. In the se- 

 cond great division, or that of Agamoiis Mollusca, we likewise 

 find two sections, grounded upon the presence or absence of an 

 apparent head. The first, Exocephala, comprises a new class, 

 calledPeltocochlides, established for the reception of the Gaste- 

 rop. Scutibranchia and Cyclobranchia of Cuvier. The second, 

 Endocephala, includes the Brachiopoda and Testaceous Ace- 

 phala of Cuvier, Lamarck's name of Conchifera being adopted 

 for the class last mentioned. 



In 1825 appeared the Malacologie \ of Blainville, who had 

 already contributed many valuable memoirs to the Journ. de 

 Physique and Bull, de la Soc. Phil, on this department of 

 zoology. No one, after Poll and Cuvier, has done so much as 

 Blainville in illustration of the anatomy of the Mollusca. At 

 the same time his arrangement, which differs in several respects 

 from all preceding ones, can hardly be considered as preferable 

 to that of the Regne Animal. It has also the disadvantage, like 

 all the rest of his system, of being attended by a peculiar nomen- 

 clature, embracing many names for the primary groups entirely 



* toin. iii. p. 317. 



•f Manuel de Malacologie et de Conchyliologie. 8vo, Paris, 1 825. The greater 

 part of this work had previously appeared in tlie Diet, des Sci. Nat. under the 

 Art. MoLLusQUEs. 



