156 HELIX-ISOMERIA. 



two equal teeth near the columella ; columellar margin dilated, cover- 

 ing the umbilicus. Alt. 14, diam. maj. 28, min. 22 mill. The larger 

 size, wholly covered umbilicus, and tooth on the upper part of the 

 outer lip are the prominent characters of this form, which is very 

 close to the typical H. bituberculata. Reeve's "H. bourcieri" (pi. 

 47, fig. 38) is probably this variety. 



Var. LATIDENTATA Miller. PI. 43, figs. 50, 51, 52. 



The two baso-columellar teeth are coalescent in this form ; the 

 umbilicus is not closed. Alt. 16, diam. maj. 32, min. 24 mill. These 

 mutations are scarcely worth names. 



H. BOURCIERI Pfeiffer. PI. 48, figs. 49-51. 



Imperforate, conoidal-semiglobose, rather thin but strong, opaque 

 blackish-brown, closely painted longitudinally with zigzag, ragged 

 stripes of cream or reddish-cream color. Surface showing under a lens 

 an excessively fine, dense, regular granulation, but apparently smooth 

 and polished. The spire is conoidal, very obtuse at apex ; the 

 sutures are moderately impressed, smooth, simple. Whorls 4J to 5, 

 the apical two corneous, very convex, planorboid ; the following whorls 

 less convex ; variegated, slowly widening, the last decidedly wider, 

 rounded-subangular at the periphery, very deeply deflexed toward the 

 aperture ; aperture subhorizontal, truncate oblong, deep purplish and 

 with a satin-like luster inside ; peristome white, broadly expanded, 

 outer and basal margins reflexed ; upper margin bearing a compressed, 

 acute denticle ; outer margin bearing a much smaller one just above 

 its junction with the basal margin, the latter with two small con- 

 tiguous tubercles in about the middle, sometimes coalescent, the inner 

 one often obsolete or subobsolete ; columella expanded and appressed 

 over the umbilicus. 



Alt. 15, diam. maj. 25, min. 201 mill. 



Alt. 13, diam. maj. 22, min. 18 mill. 



Ecuador. 



H. bourcieri PFEIFFER, Proc. Zool. Soc. Lond. 1852, p. 153 ; 

 Conchyl. Cab., p. 368, t. 130, f. 12, 13 ; Monographia, iii, p. 209 

 HIDALGO, Viage al Pacifico, Mol., p. 15. Dentellaria bourcieri 

 MILLER, in Malakozoologische Blatter 1878, p. 166. jff. bitubercu- 

 lata REEVE, Conch. Icon., f. 544. 



May be recognized at once by the beautiful color-pattern of zigzag, 

 irregular stripes of a rich cream tint on a dark purplish-brown 

 ground. 



