708 



REPORT — 1884. 



til 



fv 



Mnple fresh-water family has art equally extended range, and more than one-half 

 are confined each fo a sinfjle repfion. 



The rt'iriouH adopted hv Wallace, as already stated, are founded on the iw/c. 

 brata; he considers, however, that the distrihiition of the invertebrates is .situilnr. 

 So far as the terrestrial molliisca are concerned, I am inclined to dissent from tlii-* 

 view, lint for one circumstance tlie mollusca would afford an adniirnfile tost of 

 the tlieory liiat marine types — species, fjenera, and families — are much inf)r.- 

 widely spread than terrestrial. I am assured tliat this is tlie cii-ie, l)iit tlio 

 diflieuU;; oC j)rovini;' it arises from the fact that tiie classification of luilnioiiati! 

 terrestrial mnliusca, :is adopted hy naturalists fronernlly, is so artificial as to lie 

 worthless. (Jenera like Jlcli.r, Bulimuif, Achrtfiiui, Pupa, Vifn'iin, as nsimll\ 

 adopted, are not real genera, but associations of species united l)y chaiacters of 

 no systematic importance, and the attempts tiiat liave hitherto l)een mach; at n. 

 natural classification liave ciiieily heen founded on tlie shells, the animals iint 

 bein}^ sufliciently known for their affinities, in a very lar^re number of cases, ;n 

 ho accurately iletermined. Of late years, however, more attention has been 

 devoted to tiie soft parts of land moUusks, and in Dr. I'anl Fischer's ' .Manuel (l,> 

 OonchyliolD^'ie ' now beiuff published, a classification of tlie I'lilmonate Gastero- 

 poda is iriveii, which, althoufrh still imperfect for want of additional information, 

 13 a preat improvement upon any previously available. In this work the first 

 lliirfeen families of the Piilnmnatn Geojihila comprise all the non-operculate land 



lun 



mollusca, or 

 distributed :- 



snails and slugs, and the.se l.'J families contain 82 freiiera ti 



Peculiar to one of Wallace's land rejrions ..... /54 

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



hemisphere Vl 



(^'ommon to both hemispheres 10 



The last 10 however include Lima.v, Vifrinn, Ilfli.r, Pupa, Verfi(/o, and snm.} 



other freiiera whicli certainly need furtiier repartition. The operculated land-siiflls 



■helonginLi: to a distinct sub-order, or order, and closely allied to the ordinary 



I'rosobrancliiate Gasteropoda, are better classified, the shells in tlieir ca.se aflbrdinf.' 



■good chaiiicters. Tliey comprise four well-marlied families {IlcUcinidw, ('ijdu- 



■ffomnhr, Cj/ilop^ioridcr, and Diplominafinidcc), Ix'sides otiiers less well marked ni- 



but doul)t fully terrestrial. Not one of the families named is generally distributt'd, 



and the genera are for the most part restricted to one or two regions. Tiie portion 



of Dr. Fi.sclier's manual relating to these mollusca is unpublished, and the late?; 



general account available is that of Pfeiiler, jiublished in 18"(^' From tiii? 



monograph I ta]<e tiie following details of distribution. The number of goner.Ti 



'enumerated is 04 (iuchuUng Proserpinidce). 



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 tc 

 fiuspect that the distribution of land mollusca differs from that of land vertebrate?. 

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

 faunas tiian tliat known as Wallace's line separating the Australian and Oriental 

 regions, and running through the ^lalay peninsula between Java, Sumatra, and 

 Borneo on the one hand, and Papua witli the neighbouring groups on the otlier. 

 There is in the two regions a very great difl'erence in the vertebrate ^v-nera, nndi 

 considerubh; replacement of families. The Oriental vertcbrata contain far more 

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

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



• Monograpltia Pneumonopomorum Virentium Supp. iii. 



