1887.1 



COLLECTION FROM CHRISTMAS ISLAND. 



519 



ovate and oblique ; outer lip the least thickened within ; columellar 

 margin arcuate, slightly incrassated. 



Length 9| millim., width 5| ; aperture 5 long, 4| broad. 



The oblique form, the ridge-like lines of growth, and the coarse 

 spiral striation are the distinguishing features of this shell. 



LiTTORINA GRANICOSTATA, Sp. n. 



Shell ovate, acuminate above, white with a minute blackish apex, 

 longitudinally granosely phcate and spirally ridged and sulcated ; 

 whorls about 7, moderately convex, penultimate with about five 

 spiral ridges ornamented with small tubercles which fall one under 

 the other, producing longitudinal series and giving the shell a pli- 

 cate appearance ; last whorl with about thirteen ridges alternating 

 with very fine thread-like striae, and a large broad smooth thick- 

 ening around the base. Aperture roundish, brown within and 



Fis. 2. 



Littorina granicostata. 



finely lineated with a darker colour, with the usual basal whitish 

 zone ; outer lip crenulated at the edge, pale and ornamented with 

 the terminations of the internal brown lineatious. Columella more 

 or less arcuate, of a dark brown colour. 



Length 11 1 millim., diam. 7 ; aperture 6 long, 3| broad. A 

 shorter specimen is 10 in length, 6| in width. 



This pretty species is peculiar on account of the nodules on the 

 spiral ridges falling one under the other, thus producing longitudinal 

 series. The single shell from Christmas Island is rather young, but 

 it agrees in every particular with three adult specimens without 

 locality in Cuming's collection, from which the above description is 

 taken. 



