140 OXYSTYI.A, S01TII AMKUICAN. 



lete in places and on (lie ba>e, on a dirty flesh-tinted ground, and no 

 dark varices. though of rude, frequently arrested growth. The lip, 

 parietal wall and apex are whitish. 



From the Kio Ilachn, a series of eight specimens is before me, 

 some of which are figured, pi. 3d, tigs. 55, 5G, 57. They vary from 

 tin- typical coloring to more heavily-marked forms, and through 

 specimens with fainter and fainter stripes, to a white form with no 

 stripes, a chestnut basal band, and traces of a peripheral band. The 

 intergradation is quite complete, and could be doubted by no one who 

 saw the shells. All of them are smaller than Maracaibo specimens, 

 an average one measuring, alt. 40, diarn. '23, longest axis of aper- 

 ture 22 mill. 



Form imitator n. PI. 30, figs. 49, 50, 51, 52, 53, 54. 



From near Maracaiho we have a series of shells (pi. 30, figs. 49, 

 50, 51, 52) which vary from (1) slightly yellowish-white, absolutely 

 bandless and with no stripes; varices none, or one narrow olive line; 

 aperture white or yellowish inside, the apex, lip and parietal wall 

 white, to (2) one to three banded with brown or purplish-brown on 

 a white or flesh-tinted ground, varices, lip and parietal wall dark, apex 

 dark or white, or (3) in addition to these markings, having extremely 

 faint gray or brown longitudinal undulating stripes, apex white (fig. 

 50). Measurements are as follows : 



Alt. 52, diam. 30i, longest axis of aperture 31 mill, (albino). 



Alt. 51, diam. 30, longest axis of aperture -'.' mill. (.'!-banded). 



The young (pi. 30, tig. 52) look like O. ftrtismiri tridnctn, but 

 there is a fourth (circum-colimiellar) baud well developed. 



Exactly (lie -a me t'orin occurs at llarranguilla (pi. '.'>", figs. 53, 54), 

 the columella in these being either rather straight and stout, and the 

 spire without markings, or the columella slighter and concave, spire 



conspicuously banded ; varixed, and with a chestnut streak behind 



the \ari\. 



I'.e-ides the localities mentioned above, this form has been collected 

 at Santa Maria, in Colombia, hv ( lros>kopf: on the Magdalena ri\er, 

 by \Vallis. and in Ecuador at San Juan de la Co-la, by Dr. Reiss. 

 It occurs aluio-t e\ ervwhere \vith the striped typical form of the spe- 

 cies. Dr. von .Martens reports it, under the name tririnrln, from the 

 Marafion river, IVru. 



