PARTULA, MARIANNE ISLANDS. 315 



(/i) Length IS 1 /^, diam. 13, aperture 11 mm. long. 



Specimens of a lot consisting of rather solid shells of forms 

 b and g show a thin callus or low tubercle on the parietal 

 wall, approaching P. bicolor in this respect (figs. 5, 6). 



P. mastersi Pfr. seems to be identical with gibba, judging 

 from the description and specimens before me. It is de- 

 scribed as rather solid, buff, fleshy or violaceous, sometimes 

 banded with brown on the upper whorls. It is 17 mm. long, 

 with the aperture 10% mm. 



109a. P. GIBBA BICOLOR Pease. PI. 39, figs. 12 to 18. 



Shell solid, perforate, acutely ovate, glossy, transversely 

 marked with close obsolete stria? ; straw-colored, the whorls of 

 the spire encircled with a brownish band next to the suture. 

 Peristome brownish outside and within. Whorls 4, convex, 

 the last half the length of the shell. Peristome thickened, 

 narrowly and equally expanded. Aperture slightly oblique, 

 oval, with a small callus deep within on the belly of the penul- 

 timate whorl. Length 15, diam. 9 mm. ; aperture 5 mm. long, 

 4 mm. wide (Pease}. 



Marianne Is.: Guam (Pease, Quadras). 



Partula bicolor PSE., Amer. Journ. of Conch, vii, p. 26, pL 

 9, f. 4 (August 1, 1871). 



The above may be distinguished from P. gibba, which occurs 

 at the same locality, in being of smaller size, last whorl not 

 inflated, and in its color (Pse.). 



This form intergrades with P. gibba, and should evidently 

 be regarded as a subspecies of that, chiefly distinguished by 

 having the last whorl less swollen than in typical gibba, and 

 by having a callous nodule deep within, on the parietal wall 

 near the columella. This nodule is seen very weakly de- 

 veloped in some examples of gibba. Other supposed differ- 

 ences are even less constant. 



Pease's original description reproduced above is not good; 

 his figure is copied, pi. 39, fig. 17. The shell is rather solid, 

 with sculpture of spiral lines as in P. gibba. On the last 

 whorl these lines are very fine and close on the base, but a 



