180 PARTULA, TAHITI. 



in Fa.utaua valley, has spread all round the island, and is sub- 

 ject to so much variation that no less than fourteen species 

 have 'been proposed for the different forms. Two species 

 (P. hyalina and attenuata) are common to other islands; 

 the former is found in the Austral and on one of the Cook's 

 group ; the latter occurs on Raiatea, but does not inhabit the 

 two intermediate islands. It is a .noteworthy fact that, not- 

 withstanding both species have spread nearly all round 

 Tahiti, yet they have not developed a single varietal feature, 

 but, on the contrary, are remarkably uniform in all their 

 specific characters. 



"Here we have three species ranging round the island, and 

 all subject to the same conditions of life, yet two have not 

 shown the slightest tendency to depart from the typical forms, 

 and the other, which is very variable in its metropolis, has 

 developed many local varieties. The above facts, which are 

 common to other species, seem to suggest that physical con- 

 ditions are not the primary cause of variations, but that it is 

 the operation of some unknown law." (Garrett). 



Numerous forms of Tahiti and Moorea are sinistral. The 

 species of all the other islands are invariably dextral. Sin- 

 istral Partulae also occur in the Samoan group. 



9. P. HYALINA Broderip. PI. 24, figs. 10, 11, 12, 13. 



The shell is perforate, acutely long-ovate, thin but rather 

 strong, corneous-white or bluish-white throughout. The 

 spire is straightly conic, apex acute. Whorls 5, weakly con- 

 vex, the last convex, becoming somewhat compressed laterally 

 in the last half, base convex. Sculpture of fine growth-lines 

 decussated by minute, close spiral incised lines. . The aper- 

 ture is very oblique, ovate. Peristome rather broadly re- 

 flexed, strongly thickened within, the columellar margin 

 weakly nodose. 



Length 15, diam. 9, aperture 9 mm. 



Length 16, diam. 9i/o, aperture 9 mm. 



Society Islands : Tahiti, throughout the island in small 

 numbers (Garrett). Austral Is.: Tubuai (Grarrett), and 



