ANIMALS. 201 
internal ;1 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 /zatus between the Gasteropods and the Lamellibranchs. 
The class Gasteropoda is divisible into the following ten minor sections or Orders : 
1, Phlebenterata (Limapontias) ; 2, Gymnobranchiata (Sea Slugs) ; 3, Nucleobranchiata 
(Carinarias) ; 4, Polyplaxiphoria (Chitons) ; 5, Cyclobranchiata (Limpets) ; 6, Hypobran- 
chiata (Phyllidias) ; 7, Pomotobranchiata (Sea Hares) ; 8, Calopnoa (Land Shells, &c.) ; 
9, <Aspidobranchiata (Kar Shells); 10, Ctenobranchiata (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 difficult 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 Patellide in the order Cyclobranchiata ; but it 
differs from the family named in too many important points to be so closely united 
with it in a systematic arrangement: Ist, 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 Cir; hopodia (= Némotopodes, Blainville) to form 
his sous-type J/alentozoaires. This association is obviously erroneous ; and the position 
of 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. 
1 Three orders of Gasteropods are without shells, except in the earliest stage. 
? 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. 
4 Vide Animaux sans Vertébres, 2d ed., vol. vii, pp. 487-9. 
aa 
