COOKE : GEOGRAPHICAL DISTRIBUTION OF MOLLUSCA. 1 35 



Of the 113 Mauritian species 104 are land and 9 fresh-water. 

 Of the former, 78, of the latter none, are peculiar, while of the 

 remaining 26, 14 are common to Bourbon only, 1 to Bourbon and 

 the Seychelles, 3 to the Seychelles, and 1 to Rodriguez, leaving 

 a total of only 7 land mollusca, or about 7 per cent., occurring out 

 of the group. Such a percentage can only be paralleled in the case 

 of some of the West Indian islands, and sufficiently attests the 

 extreme isolation of Mauritius even from its giant neighbour 

 Madagascar. 



Of the 45 species known from Bourbon, 40 are land and only 

 5 fresh-water. Of the 40 land species, 18 are peculiar, and 

 14 common to Mauritius only. 



Rodriguez, as its position would lead us to expect, is more 

 isolated. Of its 23 species, 19 are land and 4 freshwater. Of the 

 former, 15 are peculiar, of the latter only one, while of the 

 4 remaining land shells, 2 are common to Mauritius only, and one 

 to the whole group. 



Of the 34 species known from the Seychelles, 27 are land and 

 7 freshwater, 21 of the former and 3 of the latter being peculiar, 

 while of the remaining 10, 6 are peculiar to the whole group. 



To put these results in a tabular form, we have : — 



Freshwater Peculiar to 



Land sp. sp. Peculiar. group. 



104 ... 9 ... 78 ... 102 (90 p.C.) 



40 ... 5 ... 19 ••■ 3S(54 P .c.) 



19 ■•• 4 ■•• 15 ■•• 21 (95 p.c.) 



27 ... 7 ... 24 ... 30 (90 p.c.) 



The mollusca of the group, regarded generally, may be considered 

 to exhibit three distinct elements — (i.) Indigenous, (ii.) Madagascar 

 (iii.) Indian and Australasian. 



(i.) Indigenous Element. The genus Pachystyia, a group of the 

 Naninidce, is quite peculiar to these islands, where it forms the main 

 portion of the land snails proper. It attains its maximum in 

 Mauritius (17 sp.), being represented by 5 sp. in Bourbon and one 

 subfossil sp. in Rodriguez, while in the Seychelles it does not occur 

 at all. But the principal feature of the Mascarene group is the 

 extraordinary development of the carnivorous genus Gibbus, which 

 is closely allied to the Ennece of tropical Africa, so largely represented 

 in the Comoros, but not in any special sense a marked feature of 

 Madagascar. Gibbus has as many as 27 species (24 pec.) in 

 Mauritius, 8 (6 pec.) in Bourbon, 4 (3 pec.) in Rodriguez; in the 

 Seychelles it is wanting, but is replaced by Edentidina and 



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