568 HISTORY OF SYSTEMS. 



evidently the author's model. It has its seven classes coi-- 

 responding pretty exactly to those founded by the author 

 of the Regno Animal ; but it has one class more, made at 

 the expense of the Pteropods ; and as all the classes are 

 presumed to be of equal value, Mr. Gray misses the natural 

 division of them into two series from the existence or non- 

 existence of a head, as Cuvier had likewise done. 



The first class embraces the Cephalopods, and the subor- 

 dinate sections correspond nearly with those already pro- 

 posed. The Pulmonata introduce the second class, — a fault 

 to be remarked also in Cuvier's method, and which has 

 arisen from not attaching sufficient importance to the sexual 

 peculiarities of the race. The other Gasteropods are ranked 

 strictly by the form and nature of the operculum, which has 

 led to certain approximations startling to those concholo- 

 gists who had settled down in the faith that it was neces- 

 sary to divide the Gasteropods only from the entire, or effuse, 

 or canaliculated state of the aperture of their shells. 



The third class is instituted to embrace two genera, — the 

 Argonauta and Carinaria, — whose position had puzzled every 

 systematist. Mr. Gray misinterpreted the puzzle also, mis- 

 led by the general resemblance there is between the shells 

 of the two genera, which are now well-known to belong to 

 different categories. The fourth class is related to the pre- 

 ceding one, and includes the Pteropods of Cuvier. There 

 has always been a difficulty in deciding by what series of 

 genera the cephalous graduate into and mingle with the ace- 

 phalous Mollusca. Lamarck decided that the Pteropods were 

 the media, emerging from a lower and arrested in their exo- 

 dus to a higher life; and M. de Ferussac judged the passage 

 to be through the class of Cephalopods. M. de Blainville, 

 throwing aside idle sjJeculation, demonstrated, by anatomical 

 research, that the transition is made by means of a small 

 number of genera related to tiie Limpets, viz., the Hippo- 

 nyx and Pileojjsis. Mr. Gray, proceeding on unassigned 

 views or, perhaps, empirically, placed the naked Acephales 

 immediately after the Pteropods, and made them lead the 

 way to the true Bivalves, — reversing that mode of develop- 

 ment which Lamarck had, wdth equal gratuity, assigned them. 



The sixth class is nearly coequal with the Conchifera of 

 Lamarck. Mr. Gray divides it into six orders from the form 

 of the foot, availing himself of the discoveries of Poll. M. 

 Goldfuss had also attempted a classification of the lamelli- 

 bvanchiate Mollusca on the same characters ; and although, 

 like Mr. Gray, he had thence been led to some happy alli- 

 ances of groups or of genera, there were other groups, on the 



