268 PARTULA, SAMOAN ISLANDS. 



Group of P. zebrina. 



57. P. ZEBRINA Gould. PI. 31, figs. 10, 11, 14, 15. 



The shell is openly rimate and perforate, rather thin, ob- 

 long-conic, scarcely shining, closely and finely striate spirally 

 throughout; marked with spots, flecks or stripes of opaque 

 buff on a corneous or brown ground, or with corneous or 

 brown on a buff ground. Spire convexly conic, the summit 

 obtuse, whorls 4 1 / 2 , convex, the second disproportionately large, 

 last whorl convex, swollen 'basally. Aperture subvertical. 

 Peristome flatly reflexed, white, thickened within with a 

 strong callous rib which ascends on the columellar margin, 

 often forming a vertical ridge near the dilated upper end. 



Length 20, diam. 12.3, aperture 12 mm. ; 4y 2 whorls. 



Length 19, diam. 12.5, aperture 12 mm. ; 4y 2 whorls. 



Length 18.5, diam. 10.7, aperture 11 mm. ; 4y 3 whorls. 



Length 21, diam. 12, aperture 12.25 mm., 4y 2 whorls 

 (tryoni). 



Samoan Is.: Tutuila (U. S. Expl. Exped. ; Schmeltz). 



Partula zebrina GOULD, Proc. Boston Soc. N. H. ii, 1848, 

 p. 196; Expedition Shells, p. 33; U. S. Expl. Exped., Moll., 

 p. 82, pi. 6, f. 89. PFR., Monogr. iii, 450. Partulus actor 

 ALBERS, Die Heliceen, 1850, p. 187. Partula actor Alb., PFR., 

 Monogr. iii, 450; Conchyl. Cab. p. 266, pi. 48, f. 13, 14.- 

 GARRETT, Proc. A. N. S. Phila, 1887, p. 133. Partula tryoni 

 HARTMAN, Proc. A. N. S. Phila. 1885, p. 204, fig. in text. 



This species is related to P. expansa, 'but differs 'by its 

 narrower, less deeply penetrating umbilicus, longer spire, and 

 especially by the spiral striation of the last whorl, which 

 was described by Gould (see fig. 11, drawn from below the 

 suture just back of the outer lip). 



The opaque buff markings appear mostly as oblique streaks 

 along the lines of growth, but they often tend to become trans- 

 formed into spirally descending stripes, especially on the 

 last half whorl, approaching the condition of the further 

 evolved P. expansa. Often the cream tint predominates over 

 the corneous or brown markings, which remain as streaks 

 or spots. 



