PARTULA. 127 



to intergrade with any other forms, the young being always dextral in whorl, 

 and of a white milky color very similar to the adult shell. Figs. 3-8 rep- 

 resent mere color varieties of one and the same species (P. otaheitana). 

 Snails of the types o£ Figs. 3 and 5 are very common in all four valleys. 

 Fig. 4 represents an extremely dark-brown individual found in TipsBrui val- 

 ley. No other individual was found which displayed tiiis degree of melanic 

 coloration, although many were found of a hue intermediate between Figs. 

 4 and 5. The pink-tipped snails illustrated in Fig. 8 are common in Ha- 

 muta valley, but are not very abundant in Fautaua or Piraj valleys, and 

 were not discovered in Tipterui valley. Figs. 6 and 7 represent a pecu- 

 liar color variety (P. otaheitana var. lignaria) which is evidently derived 

 from the snails shown in Figs. 3, 4, 5, and 8 ; for some of the young 

 taken from snails of the type of Figs. 6 and 7 resemble the normal 

 young ^ of types 3, 4, 5, and 8, while some of the young of the latter exhibit 

 the whorl-stripes characteristic of the normal young of Figs. 6 and 7. 

 The snails of the type of Figs. 6 and 7 occur in the same valleys as their 

 close relatives of the types of Figs. 3, 4, 5, and 8, and it is not improbable 

 that their tendency to generate a whorl-striped variety is swamped by fre- 

 quent inter-crossing with the unstriped snails of the same valleys. Were 

 they isolated, it seems probable that they would soon initiate a new race, 

 and in time perhaps a distinct species. 



Partula h//alina, Figs. 1, 2. PartuJa nodosa var. sinistralis. Figs. 14, 15. 



Maniapoo Valley. 



Maruapoo valley is situated on the western side of Tahiti, about seven 

 miles south of Tipa^rui valley, from which it is separated by at least seven 

 ridges. Of the two species of snails found in Maruapoo, only one is common 

 to both Tipa3rui and Maruapoo. This one is the translucent milky-white 

 species, P. hyalina, represented in Figs. 1 and 2. The predominant species 

 of Maruapoo, P. nodosa Pfeiffer, var. sinistralis, is represented in Figs. 14 

 and 15, and constitutes 99 per cent of the snail-fauna of the valley. The shell 

 is blunt in shape, and the spire is short. The lip is quite thick, and is usually 



' The term "normal young "is applied to any young snail which is similar in color to the adult 

 which bore it. 



