HELIX-OBBA. 211 



below, ornamented with a brown band at the suture and a white one 

 at the periphery, the base pale, subcompressed around the moderate, 

 conical umbilicus ; aperture scarcely oblique, subtriangular-luuar ; 

 peristome thick, white, expanded and reflexed, margins remote, 

 joined by a thick callus. Alt. 18, greater diam. 37, lesser 31 mill. 



Philippine Is. 



H. avus PFR. P. Z. S. 1852, p. 83 ; Mon. Hel. Viv. iii, p. 251 ; 

 Conchyl. Cab. p. 473, t. 157, f. 12-14. REEVE, Conch. Icon. f. 658. 



The aperture is less oblique than is usual in Cammna, and it may 

 prove to belong elsewhere when the characters of the nucleus are 

 determined. 



Subgenus OBBA Beck, 1837. 



Obba BECK, Index Molluscorum, p. 30, (species, H. planulata, 

 papilla, mamilla). ALBERS, (edit, von Martens,) Die Heliceen, p. 

 158, (type H. mamilla Fer.), I860. 



Shell umbilicate (rarely covered) globose, globose-depressed or 

 lens-shaped, often carinated ; apex very obtuse, the earlier \\ or 2 

 whorls forming a polished nucleus. Aperture generally very oblique 

 or horizontal ; peristome expanded, basal margin reflexed. 



Beck did not indicate which of the three species enumerated by 

 him should T)e regarded as the type of Obba. We are therefore at 

 liberty to accept H. mamilla as the type following Albers' classic 

 work. 



This subgenus was accurately defined and limited by Von 

 Martens in the second edition of Albers' Die Heliceen. Obba may 

 be divided into three well-marked sections : 



Section OBBA, s. s. 



Shell rudely sculptured, the sculpture oblique to lines of growth ; 

 solid ; peristome thickened, the ends converging, joined by a cord 

 of callus ; brown, or with 1 or 2 light bands. 



Section OBBINA, Semper. 



Shell striate or wrinkled in the direction of growth-lines ; last 

 whorl very deeply deflexed in front ; aperture subhorizontal, ends 

 of peristome converging, continuous across the parietal wall ; white 

 or light colored, banded or speckled with brown. 



