240 PARTULA, RAIATEA AND TAHAA. 



of faba and fusca. G-arrett writes that "hybrids between this 

 species and fusca and faba are very frequent." 



The typical coloration of navigatoria (fig. 9, copied from 

 Reeve) and the synonymous variabilis is yellow, profusely 

 streaked with chestnut, the spire often pinkish. This is the 

 normal or usual form. Other patterns are: 



Uniform yellow. Not common. 



Uniform dark chestnut, or with pale apex. Not 'common. 



The last form, greenish yellow, the base and a subsutural 

 band chestnut, is not uncommon; it resembles typical P. 

 faba in pattern. 



' * The parietal tooth mentioned by Pf eiffer, but not alluded 

 to by Reeve or Pease, is not constant, but exists in about two- 

 fifths of the adults. The former author's 'medio subden- 

 tato,' likewise not mentioned by the latter two writers, is 

 simply the lower angle of the small labial sinus. 



"In shape it varies from ovate to oblong-ovate, as the fol- 

 lowing two measurements will show: Length 25, diam. 

 13 mm.; length 20, diam. 13 mm." (Garrett). 



38. P. FUSCA Pease. PI. 17, figs. 5, 6, 7. 



' * Shell umbilicated, solid, varying from an abbreviate-ovate 

 to oblong-ovate, roughly striated by irregular lines of growth, 

 and the usual fine spiral incised lines become evanescent on 

 the body-whorl; spire convexly conical, less than half the 

 length of the shell ; suture linearly impressed, frequently mar- 

 gined by a thread-like white line; whorls 5-6, more or less 

 flatly convex, last one large, convex, rounded or turgid, some- 

 times slightly angled just above the aperture; base more 

 openly umbilicated than usual in the ground species; aper- 

 ture subvertical, oblong, sides nearly parallel ; parietal region 

 more or less glazed with callus, and sometimes dentate ; peris- 

 tome rather broadly expanded, moderately thick, slanting, 

 flat or concave, strongly incrassated within and sinuous 

 above ; columellar lip depressed, receding or transversely 

 grooved above. Color very variable : whitish corneous, straw- 

 yellow, fulvous, light or dark chestnut, sometimes brown- 



