XI MADAGASCAR — THE MASCARENES 



337 



Land and Fresh-water Mollusca of Madagascar 





Ennea ... 9 Leucotaenia . 2 Melania ... 7 Cyclostoma 



. 54 



Urocyclus . . 2 Clavator . . 2 Melanatria . . 4 Otopoma . 



. 5 



Helicarion (?) . 1 Achatina . . 3 Paludomus . . 2 Lithidion , 



. 1 



Macrocyclis (?) 1 Opeas ... 2 Vivipara. . . 1 Acroptychia 



. 3 



Kaliella ... 1 Subulina . . 3 Bithynia . . 2 Hainesia . 



. 3 



Nanina (inc. sed.) 9 Vaginula . . 4 Cleopatra . . 2 Unio . . . 



. 1 



Ampelita . . 35 Limnea ... 2 Ampullaria . . 6 Corbicula . 



. 2 



Helicophanta . 17 Planorbis . • 3 Cyclophorus . 2 Sphaerium . 



. 1 



Pachnodus . . 2 Isidora ... 3 Cyclotus (?) .1 Pisidium . 

 Rachis ... 2 



. 1 



The Comoro Islands. — This isolated group possesses about 

 100 species, almost all of which are peculiar. The principal 

 feature is the rich development of Ennea (30 sp.). On the whole 

 the group shows more relationship to Madagascar than to the 

 mainland. Thus we have six species of true Cyclostoma., and 

 only one Achatina^ while among the fresh-water genera is 

 Septaria^ which is characteristic of the whole Malagasy Sub- 

 region, but is absent from the mainland. The Helicidae are all 

 of insignificant size. Peculiar to the group is the remarkable 

 genus Cyclosurus (Fig. 152, p. 247). 



(5) The Mascarene Province (Mauritius, Bourbon, Rodriguez, 

 and the Seychelles). — The percentage of peculiar species, which 

 is very high, can only be paralleled in the case of some of the 

 West Indian islands, and sufficiently attests the extreme iso- 

 lation of the group from Madagascar. We have — 









Fresh-water 





Peculiar to 





Total sp. 



Land sp 



sp. 



Peculiar 



group 



Mauritus . 



. 113 



104 



9 



78 



102 (90 p.c.) 



Bourbon . 



. 45 



40 



5 



19 



38 (84 p.c.) 



Rodriguez . 



. 23 



19 



4 



15 



21 (95 p.c.) 



Seychelles . 



. 34 



27 



7 



24 



30 (90 p.c.) 



The Mollusca of the group exhibit three distinct elements, 

 the Indigenous, the Madagascan, and the Indian and Australa- 

 sian. 



The genus Pachystyla (Naninidae) is quite peculiar, forming 

 the main portion of the land snails proper. It attains its maxi- 

 mum in Mauritius (17 sp.), with 5 sp. in Bourbon and one 

 sub-fossil sp. in Rodriguez, while in the Seychelles it is absent. 

 But the principal feature of the Mascarene group is the extraor- 

 dinary development of the carnivorous genus Gribhus^ which 



