314 PARTULA, MARIANNE ISLANDS. 



color. The last three whorls have an opaque white 'border be- 

 low the suture. The last whorl varies in the degree of swell- 

 ing, and in small individuals is usually angular in front, at 

 the periphery; base very full and convex. Umbilicus small 

 and deep, more rounded than usual in Partula. The engraved 

 spiral lines are distinct and not very close above the periphery, 

 more crowded on the base. The aperture is oblique, white in- 

 side in the pale, variously colored in the dark varieties. The 

 peristome is white, or in some forms flesh-tinted. The outer 

 lip is expanded, rather heavily thickened within, the callus 

 somewhat abruptly terminating at the beginning of the curve 

 to the upper insertion; columellar lip dilated. Pigs. 2, 3, 

 5 and 6 represent individuals of the typical P. gibba. Be- 

 sides the typical coloration (a) described above, there are 

 shells with (&) reddish spire and brown last whorl (fig. 2), 

 and others (c) of the typical pale tint and a white spire (fig. 

 9). These forms occur together in some lots before me. 

 Other forms are: 



(d) Corneous-white, somewhat transparent, very thin (pi. 

 39, fig. 11). 



(e) Drab with the spire dull dark purple, lip fleshy (fig. 7). 

 (/) Lilac, the spire darker, aperture brown within (fig. 8). 

 (g) Light reddish-brown (fig. 5). 



(h) First 2y 2 whorls bicolored, brown and whitish, the rest 

 corneous-yellow, becoming dull purple near the lip. Interior 

 lilac, with a brown streak within the lip, which is flesh-colored 

 (fig. 10). 



There is considerable variation in the solidity of the shell, 

 and the thickness of the lip-callus. The latter is sometimes 

 perceptibly nodulous, as in fig. 6. 



To what extent the variations in color and texture are local 

 or racial is unknown. All have a white sutural border. Ex- 

 amples measure as follows : 



(a) Length 17, diam. 11.3, aperture 9.8 mm. long. 



(d) Length 17, diam. 12, aperture 10 mm. long. 



(e) Length 15%, diam. 11, aperture 9 mm. long. 



(/) Length 18~y 2 , diam. 12%, aperture, 10 mm. long. 



