﻿NO. 14 LANDSHELLS COLLECTED IN PERU IN I9II — DALL 9 



shells. By breaking or grinding away the outer wall of the later 

 whorls and revealing the hidden lamination, it is seen to be quite dif- 

 ferent in the two forms. As often happens in Holospira a similar 

 exterior masks two very unlike interior arrangements. 



In the present species instead of beginning abruptly and reaching 

 its greatest extension in the first half of the last whorl as in infundib- 

 ulum, the lamina begins gradually near the base of the pillar wall 

 and rises for a third of a whorl before beginning its strongest de- 

 velopment, when it forms a remarkably stout horizontal lamina with 

 a broad, flat edg^e almost touching the outer wall, and, rising ob- 



Fig. 1 Fig. 2 



Fig. 1. — Ataxus umbilicatellus , part of front wall removed showing hidden 

 lamina. 3/1. 



Fig. 2. — Ataxus umbilicatellus, part of shell removed showing opposite view 

 of lamina. 3/1. 



liquely in the lumen of the penultimate whorl, continues in the angle 

 between the axial wall and the roof of the whorl. Then it suddenly 

 becomes thin, and immediately low, and continues in the ante- 

 penultimate whorl as little more than a sharp raised thread. 



The peculiarities of this spiral lamina as observed in the several 

 species, include its beginning so far back from the aperture, its near 

 occlusion of the passage when at its strongest, the enlargement or re- 

 curvation of the distal edge, the curious oblique course not parallel 

 with the gyre of the whorls, and, in the more elongated forms, of the 

 duplication or repetition of the expansion at different points in the 

 spire. Its function is probably protective, as it almost closes the 

 aperture, and the animal can retreat behind the most obstructive 

 portion. 



