ANIMALS. 201 



internal ;i single or divided, and conical or spiral in the first case ; and more or less 

 rudimentary in the second."" 



In accordance with the prevailing view, the present division is herein considered 

 to be co-ordinate with the last, and placed in the same great section of the Molluscous 

 sub-kingdom. Viewing it in all its modifications, there cannot be said to be more than 

 an approximate connexion between the two divisions ; in short, there appears to be an 

 impassable hiatus between the Gasteropods and the Lamellibranchs. 



The class Gasteropoda is divisible into the following ten minor sections or Orders : 

 1, Fhlebenterata (Limapontias) ; 2, Gymnohrancldata (Sea Slugs) ; 3, Nucleobranchiata 

 (Carinarias) ; 4, Folyplaxiphoria (Chitons) ; 5, Cyclobranchiata (Limpets) ; 6, Hypobran- 

 chiata (Phyllidias) ; 7, Pomotobranchiata (Sea Hares) ; 8, Coclopnoa (Land Shells, &c.) ; 

 9, Jspidobranchiata (Ear Shells); 10, (Jtenobranchiata (Whelks); and 11, Cirrho- 

 branchiata (Tooth Shells).^ The probability is, that most of these orders have existed 

 during all the organic periods of our planet ; but, owing to various circumstances, 

 especially to some being without any enduring ■■ remains, their chronogeny will long 

 remain one of the most difiicult problems in Malacology. As yet only three orders, 

 the fourth, tenth, and eleventh of the above list, are known to have existed during the 

 Permian epoch. 



Order Polyplaxiphoria, De Blainville. 



This group is usually associated with Patellida in the order Cyclobranchiata ; but it 

 difi'ers from the family named in too many important points to be so closely united 

 with it in a systematic arrangement : 1st, the shell is divided ; 2d, the gills are in the 

 form of triangular leaflets ; 3d, the margin of the mantle is thick, and generally extended 

 beyond the shell ; 4th, the muscular system is much and complexly divided ; 5th, the 

 generative organs have two openings; 6th, the head is projecting; 7th, there are no 

 tentacles ; and 8th, there are no eyes.'' De Blainville elevated Polyplaxiphoria to the 

 rank of a class, and associated it with Oir/hopodia {=. Nemofopodes, Blainville) to form 

 his sous-type Malentozoaires. This association is obviously erroneous ; and the position 

 oi Polyplaxiphoria appears to be too elevated. But there seem not to exist any serious 

 objections to our considering the group as of co-ordinate value with the other orders 

 included in the present class. 



^ Three orders of Gasteropods are without shells, except in the earliest stage. 



2 Slightly altered from Sander Rang. (Vide Manuel des Mollusques, p. 119.) 



3 The hybrid names of Cuvier are herein discarded for the more classically constructed ones of 

 Schweigger. 



* Vide Animaux sans Vert^bres, 2d ed., vol. vii, pp. 487-9. 



aa 



