122 EXPEDITION OF THE "ALBATROSS," 1899-1900. 



are usually dextral or sinistral respectively, but this is not invariably the 

 case. It is interesting to observe, however, that all of the }-oung developed 

 within any given adult are either dextral or sinistral, never some of them 

 dextral and others sinistral. The young are born one at a time ; three 

 eggs and two or three young snails in various stages of development being 

 often found in a single adult animal. At the time of birth the shell of the 

 young one comprises two and a half whorls. No young are developed 

 until after the lip of the adult shell has been completely formed. 



Partula hyalina Brodepjp. 



Fkjs. 1, 2; I'^-T. 



This snail is found in all six valleys, but is never abundant ; constituting 

 but 2J per cent of the total number of snails in Pir*, 3 per cent in Hamuta, 

 12 per cent in Fautaua, 7 per cent in Tipajrui, 1 per cent in Maruapoo, and 

 2 per cent in Vaihiria valley. It is readily distinguished from all the other 

 snails by its milky-white, translucent shell, and the absence of a tooth upon 

 the columella. Every individual found is dextral, as are also the young 

 taken from the adults. In all forty-four specimens were obtained, and 

 nineteen of these yielded fifty-five young snails. The young are all white 

 in color, and show no tendency to intergrade with the young of any other 

 species, hence we conclude that this is a true species separate and distinct 

 from any other snail of tlie six valleys. 



PaKTULA OTAHEITANA BrUGUIEEE. 



Figs. 3-8. 



Plrcv, ITumida, Fautaua, and Tipmrid Valleys. The relationships of the color- 

 types represented in Figs. 3, 4} ^y '^'"■^ 8. 



These forms, which are represented in Figs. 3, 4, 5, and 8, are mere 

 color varieties of one and the same species. They are found in l*ira\ 

 TLuimta, Fautaua, and Tipoerui valleys, but appear not to exist in ]\Iarua- 

 poo or Vaihiria. Fig. 3 represents the lightest colored type, where the 

 entire shell is of a hornv-yellow hue, while Fig. 4 repi-esents the darkest 

 type, the shell being of a imiform rich brown. In Fig. 5 we see a horny- 



