90 PARTULINA, SECTION BALDWINIA. 



Section BALDWINIA Ancey. 



Baldwinia ANCEY, Proc. Malac. Soc. London, iii, p. 270, 

 July, 1899. 



Shell sinistral (except in P. dubia), perforate, thin, ovate- 

 acuminate or ovate-conic, with the color and sculpture of 

 Partulina; lip narrowly expanded, but little thickened ; colu- 

 mella somewhat twisted but without a callous fold or tooth. 

 Type A. physa Nc., 1855 = A. confusa Sykes. 



Baldwinia differs from Perdicella by its larger size and 

 enlarged last whorl, giving the shell a conic form. It is no 

 doubt, like Perdicella, a derivative of Partulina, which has 

 the same sculpture and color-patterns. 



It is quite likely that the Baldwinias of Hawaii, Maui and 

 Oahu are so many independent derivatives from the Partu- 

 lina stock, but until this is demonstrated it is simpler to group 

 them together. In any case the forms of Hawaii and Oahu 

 are in all probability the descendants of emigrants from the 

 Maui-Lanai-Mo'lokai center. Whether the degeneration of 

 the columellar fold was expressed in the original stock is un- 

 certain, since its degeneration is without doubt a secondary 

 modification. The presence of Partulinoid forms in Oahu 

 seems anomalous, but the distribution of Laminella and Ptero- 

 discus also show that there was a limited amount of inter- 

 change between the Oahu and the Maui-Lanai-Molokai centers 

 after the modern groups had become differentiated. 



Species of Baldwinia. 

 1. Hawaiian species. 



a. Aperture much more than half the shell's length; shell 

 white or banded, without axial or oblique color streaks ; 

 surface smoothish, finely striate, last whorl much in- 

 flated. P. horneri, no. 47. 

 a 1 . Aperture slightly more half the length; last whorl 

 rather roughly striate ; length over 20 mm. 



P. confusa, no. 46. 



a 2 . Aperture about half the length ; shell variously banded 

 or streaked, smoothish; densely striated spirally 

 throughout, length less than 20 mm. P. physa, no. 48. 



