TRANSACTIONS OF SECTION C. 



709 



ns Cyclophorm, Ci/chitus, Leptojxnna, rupiiielln, pHj)iun, Diplminiifitiiirf, and //c//- 

 riW, nil found in tliu Oriental rt'j^ion.and nmstlv cliarncterislicof it, wliil.st tiie (inly 

 vtfculiar types known are L(>ucoj)fi/c/ii(r,v\<m'\y allied toLeptopomn, from Now (iuinca, 

 and Jlctcnxi/rluf, a])parontly related to tli« Indian C'lfat/inpoma, from New Cale- 

 donia. Farther east in Polynesia there ait! some very rtfmarkahle and i)eculiHr types 

 (if land-shells, such aa AchatinvUa, liui these do not extend to Australia or Papua. 

 <)n thtMithtr hand searcely a single Oiienfal <.'cnus extends to Africa, the terrestrial 

 -.uolluscan fauna of which eontinentdilfers fur more from that of the Oriental regiou 

 ihan tlie latter does from that of tropical Australia. 



The pamo is the case with plants. In an important work lately published 

 \w Dr. (•. Drude, of Dresden, the tropics of the Old World are divided into three 

 distiact reifions— (1) tropical Africa; (li) the Ka.st African islands, .Mada>,'ascar, 

 kc,\ (.'<) India, South-Eastern Asia, tiie Malay archipelago, Northern Australia, 

 and Polynesia. 



A very large proportion of the families and even of the genera of marine 

 inoUusca are almost of world-wide distribution, and even of the tropical and 

 >.ubtroi)ical genera the majority are found in all tli«! warmer seas. I liavo 

 no recent details for the whole of the marine mollusca, but a very fair comparison 

 with tlie data already given for land-shells may be obtained from the lirst L*5 

 families of I'rosobranchiate (tasterojjoda, all that are hitherto ])ubli9hed in 

 risclier's manual. These '2G families include Coniihc, Olivida, Volutid'C, UnccinidcCf 

 Muricidte, C'l/prcidcp, Stru)nhid<p, CerithiidfO, I'lana.iuhp and their allies, and 

 contain 110 living marine genera, the known range of which is the following — 



Found only in the Atlantic Ocean 



Found only in the Pacitic or Indian Ocean, or both 



Found only in Arctic or Antarctic Seas, or in both 



I'^ound in tlio warmer parts of all oceans . , 

 ^\'idely, and for the most part uuivensally, distributed 



15 

 12 



-55 



84 



27 



-Gl 



That is r)2-0 per cent, are found in both hemispberes, whilst only lO'S per cent, of 

 the inopercuiato, and 12-5 per cent, of the operculato land mollusca, have a 

 tiinilar distribution. This is, however, only an imperfect test of the diflerence, 

 which is really much greater than these numbers named imply by themselves. 



Some genera of fresh-water mollusca, as Unto, Anodun, Ci/clas, Lynmea, 

 Tliinorbis, Pcdtidina, and Bythinia, arc very widely spread, but a much larger number 

 are restricted. Tims if Unio and Aimdon are extensively distributed, all allied fresh- 

 water genera, like Motiorondi/kra, Mycrtnpns, Iridina, Spathn, Castalia, ylit/ieria, 

 and Miillcria inhabit one or two regions at the most. The same result is not 

 found finm taking an equally important group of marine mollusca, such as Vcnerida 

 or Curdiadce. 



Throughout the marine invertebrata, so far as I know, the same rule holds 

 crood: a few generic types are restricted to particular sens; the majority are 

 found in suitable ha])itats throughout a large portion of the globe. The marine 

 provinces that have been hitherto distinguished, as may be seen by referring to 

 those in Woodward's 'Manual of the Mollusca,' or Forbes and Godwin Austin'.^ 

 * Natural History of the European Seas,' or Fischer's ' Manuel de ('onchyliologie,' 

 or Agassiz's 'Revision of the Echini,' are founded on specific distinctions, whilst 

 the terrestrial regions are based on generic diH'erences, and often on the presence 

 or absence of even larger groups than genera. 



Botany ofl'ers a still more remarkable example. I have just referred to 

 Br. Oscar Drude's work,' published within the last few months, on the distribution 

 of))lants. Dr. Drude divides the surface of the globe into four groups of floral 

 regions i^Florenreichsyruppe), and the.«? again into floral regions (Fhrcnreiche), 

 lo in number, which are again divided into sub-regions {Gebiete). The first group 

 cf floral regions is the oceanic, comprising all the marine vegetation of the world ; 



' Petcrmann's Mitthcilwigen, Ergunzungsheft No. 74, ' Die Florenreiche dor Erde.* 



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