PARTULA. 123 



brown shell streaked longitudinally with darker brown, while Fig. 8 

 sliows a light horny-brown shell having the apex tinged with pink. Many 

 individuals which are intermediate in color between these various forms 

 are found. An idea of the relative abundance of these color varieties in 

 the different valleys may be obtained through an inspection of Table I. 

 at the end of this paper. 



Shells of the color-type represented in Fig. 3 are abundant in all of the 

 four valleys, but are especially characteristic of Pirae, where they constitute 

 58 per cent of the entire number of snails found in the valley. 



Fig. 4 is drawn from the darkest snail obtained in Tipterui valley. 

 It contained two young which were much lighter in color than their parent, 

 and resembled the young commonly found in snails of the type represented 

 by Fig. 5. 



Snails of the type of Fig. 5 are abundant in Hamuta, Fautaua, and 

 Tipa?rui valleys, where they constitute 47, 62, and 53.5 per cent, respec- 

 tively, of the shells found in each valley. In Pirae valley, however, they 

 are not so abundant, constituting but 19 per cent of the snails found. 



Fig. 8 represents a snail which resembles Fig. 3, excepting that the 

 apex of the shell is tipped with pink.^ It is remarkable that in Hamuta 

 valley 63 per cent of the snails of the types shown in Figs. 3 and 5 are pink- 

 tipped. In Pirae and Fautaua 9.5 per cent and 30 per cent respectively of 

 these snails are pink-tipped, while in Tipa^rui valley none of them display 

 this peculiarity. This as well as all the other evidence which we have 

 collected concerning the biology of the Tahitian snails leads one to believe 

 that the constitutions and inherited tendencies of the snails of any given 

 Vidley are quite different from those of the snails of any other valley ; 

 for it would be difficult on any other grounds to account for the fact that 

 the horny epidermis is readily disintegrated in Hamuta, while it resists 

 weathering almost perfectly in Tipajrui valley. 



In Tipaerui valley all of the snails represented in Figs. 3, 4, 5, and 8 

 are dextral, while in Pirae valley they are all sinistral. In the two inter- 

 mediate valleys, Fautaua and Hamuta, however, the snails are some of 

 them dextral, others sinistral. For example, in Fautaua valley 54 per cent 



' Tliis pink coloration is due to the partial disappearance of the outer I'pidermis of the sliell. 



