708 report — 1884. 



single fresh-water family has an equally extended range, and more than one-half 

 are confined each to a single region. 



The regions adopted by Wallace, as already stated, are founded on the verte- 

 brata ; he considers, however, that the distribution of the invertebrates is similar. 

 So far as the terrestrial mollusca are concerned, I am inclined to dissent from this 

 view. But for one circumstance the mollusca would afford an admirable test of 

 the theory that marine types— species, genera, and families — are much more; 

 widely spread than terrestrial. I am assured that this is the case, but the' 

 difficulty of proving it arises from the fact that the classification of pulmonate 

 terrestrial mollusca, as adopted by naturalists generally, is so artificial as to be' 

 worthless. Genera like Helix, Bulimus, Acliatina, Pupa, Vitrina, as usually 

 adopted, are not real genera, but associations of species united by characters of 

 no systematic importance, and the attempts that have hitherto been made at a. 

 natural classification have chiefly been founded on the shells, the animals not 

 being sufficiently known for their affinities, in a very large number of cases, to 

 be accurately determined. Of late years, however, more attention has been; 

 devoted to the soft parts of land mollusks, and in Dr. Paul Fischer's ' Manuel de 

 Conchyliologie.' now being published, a classification of the Pulmonate Gastero- 

 poda is given, which, although still imperfect for want of additional information, 

 is a great improvement tipon any previously available. In this work the first 

 thirteen families of the Pulnionata Geophila comprise all the non-operculate land 

 mollusca, or snails and slugs, and these 13 families contain 82 genera thus 

 distributed : — 



Peculiar to one of Wallace's land regions 54 



• Found in more than one, but not in both America and the Eastern 

 hemisphere .......... 12 



Common to both hemispheres ....... 16 



The last 16 however include Limax, Vitrina, Helix, Pupa, Vertigo, and some 

 other genera which certainly need further repartition. The operculated land-shells 

 [belonging to a distinct sub-order, or order, and closely allied to the ordinary 

 ProsobraricHiate Gasteropoda, are better classified, the shells in their case affording 

 igood characters. They comprise four well-marked families (Hdicinidce, Cyclo- 

 stbmidce, Cyclophoridce, and Diplommatimdat), besides others less well marked or 

 but doubtfully terrestrial. Not one of the families named is generally distributed, 

 and the genera are for the most part restricted to one or two rep-ions. The portion' 

 of Dr. Fischer's manual relating to these mollusca is unpublished, and the latest 

 general account available is that of Pfeiffer, published in 1876.' From this 

 monograph I take the following details of distribution. The number of genera, 

 enumerated is G4 (including Proserpinida). 



Peculiar to one of Wallace's land regions 48 



Found in more than one, but not in both America and the Eastern 

 hemisphere .......... 8 



Common to both hemispheres 8 



It is the distribution of the terrestrial operculate mollusca which induces me to* 

 suspect that the distribution of land mollusca differs from that of land vertebrates- 

 One instance I may give. There is nowhere a better marked limit to two vertebrate 

 faunas than that known as Wallace's line separating the Australian and Oriental 

 regions, and running through the Malay peninsula between Java, Sumatra, audi 

 Borneo on the one hand, and Papua with the neighbouring groups on the other. 

 There is in the two regions a very great difference in the vertebrate genera, and a 

 considerable replacement of families. The Oriental vertebrata contain far more 

 genera and families common to Africa than to Australia. Now, the operculate 

 laud-shells known from New Guinea and Northern Australia belong to such genera. 



1 Monograpltia Pneumonopomorum Viventium Supp. iii. 





