MILNE-EDWARDS. 589 



** The respiratory chamber open, viz. the front edge of 

 the mantle is free from the back of the neck, leaving a 

 large slit for the admission of the air into the bag. 

 An operculum. 



The families are 1. Cyclostomidas ; 2. Helicinidag. 



There can, I think, be only one opinion as to the great 

 merits of this method, of which the author has given a most 

 interesting exposition in the work referred to, one of small 

 price and easy access. Its superiority as a whole to any 

 previous one can scarcely be questioned ; and the new views 

 taken as to the position of several of the families in their 

 respective orders, as well as in regard of the genera which 

 are made to enter into the composition of the families, 

 nothing less than the most extensive and critical knowledge 

 of the entire class could have suggested. The method, Mr. 

 Gray says, " is founded on the examination of the animals of 

 all the molluscans contained in the London and Paris collec- 

 tions, as well as of all the drawings or engravings of the 

 animals which I have been enabled to see, exceeding more 

 than five thousand species, being at least one hundred times 

 as many animals as were known when Lamarck proposed his 

 system, and fifty times as many as were known to Cuvier 

 when he published his system on the Animal Kingdom."* 

 The defects of it proceed from having had the attention too 

 exclusively directed to the exterior anatomy of the animal 

 irrespective of the form of the shell ; whence it has resulted 

 that the Haliotidae are found alongside of the Trochusidae, 

 although their relationship is really distant, as Cuvier had 

 proved. Other, and not less prominent, instances of mis- 

 alliance might be pointed out, but the one selected has been 

 made more apparent and decisive of late by the researches of 

 Milne-Edwards and Emile Blanchard ; and these researches, 

 again, have effected a revolution in the arrangement of the 

 class, which will, probably, receive the adhesion of future 

 naturalists. 



From the more or less perfect formation of the foot, which 

 regulates the motions and much of the economy of the 

 animal, Milne-Edwards proposes to divide the Gasteropoda 

 into two subclasses, viz. 1. the normal Gasteropods, em- 

 bracing the Pulmones, Nudibranches, Inferobranches, Tecti- 

 branches, Pectinibranches, Scutibranches, and the Cyclo- 

 branches of Cuvier ; and 2. the aberrant Gasteropods or 

 Heteropodes of the same author. 



* Proceed. Zool. Soc. Lond. No. 178, p. 132. 



