TRANSACTIONS OF SECTION C. 709 



as Cyclophorus, Cyclotus, Leptopoma, Pupinella, Piipina, Diphmmatina , and Heli- 

 cina, all found in the Oriental region, and mostly characteristic of it, whilst the only 

 'peculiar types known are Leucoptychia, closely allied to Leptopoma, from New G uinea, 

 and Heterocyclics, apparently related to the Indian Cyathopoma, from New Cale- 

 donia. Farther east in Polynesia there are some very remarkable and peculiar types 

 of land-shells, such as Achatinella, but these do not extend to Australia or Papua. 

 <On the other hand scarcely a single Oriental genus extends to Africa, the terrestrial 

 amollusean fauna of which continent differs far more from that of the Oriental region 

 than the latter does from that of tropical Australia. 



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

 by Dr. O. Drude, of Dresden, the tropics of the Old World are divided into three 

 distinct regions— (1) tropical Africa; (2) the East African islands, Madagascar, 

 &c. ; (3) India, South-Eastern Asia, the Malay archipelago, Northern Australia, 

 and Polynesia. 



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

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

 •subtropical genera the majority are found in all the warmer seas. I have 

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

 with the data already given for land-shells may be obtained from the first 25 

 families of Prosobranchiate Gasteropoda, all that are hitherto published in 

 Fischer's manual. These 25 families include Conidce, Olividce, Volutidce, Buccinidce, 

 Muricidce, Cypreidce, Strombidce, Cerithiida, Planaxidce and their allies, and 

 contain 116 living marine genera, the known range of which is the following — 



Found only in the Atlantic Ocean ...... 15 



Found only in the Pacific or Indian Ocean, or both . . .28 

 Found only in Arctic or Antarctic Seas, or in both . . .12 



—55 

 Found in the warmer parts of all oceans . . . , ,34 

 Widely, and for the most part universally, distributed , , .27 



—61 



"That is 52 - 6 per cent, are found in both hemispheres, whilst only 19*5 per cent, of 

 the inoperculate, and 12-5 per cent, of the operculate land mollusca, have a 

 j-imilar distribution. This is, however, only an imperfect test of the difference, 

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



Some genera of fresh-water mollusca, as Unio, Anodon, Cyclas, Lymnea', 

 Tlanoi-bis, Paludina, and Bythinia, are very widely spread, but a much larger number 

 ■are restricted. Thus if Unio and Anodon are extensively distributed, all allied fresh- 

 water genera, like Monocondylcea, Mycetopus, Iridina, Spatha, Castalia, JEtheria, 

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

 found from taking an equally important group of marine mollusca, such as Veneridce 

 or Cardiadce. 



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

 good: a few generic types are restricted to particular seas; the majority are 

 found in suitable habitats 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's 

 4 Natural _ History of the European Seas,' or Fischer's ' Manuel de Conchyliologie,' 

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

 the terrestrial regions are based on generic differences, and often on the presence 

 or absence of even larger groups than genera. 



Botany offers a still more remarkable example. I have just referred to 

 Dr. Oscar Drude 's work, 1 published within the last few months, on the distribution 

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

 Tegions (Florenreichsyruppe), and these again into floral regions (Florenreiche), 

 15 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 ; 



• Petermann's Mttheilungen, Erganzungsheft No. 74, ' Die Florenreiche der Erde.* 



