﻿2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 59 



mental lines ; the aperture is very similar to that of P. labyrinthus 

 and is best described differentially ; in both the thickened peristome 

 partly overshadows the deep umbilicus, but in P. goldmani the com- 

 missure is prolonged and turned upward into the umbilicus, nearly 

 reaching the suture of the last whorl ; the upper part of the peristome 

 is in line with the parietal lamina and nearly parallel with the oppo- 

 site part of the peristome, while in P. labyrinthus the parietal lamina 

 meets the peristome at a right angle and the area included by the 

 lamina and peristome is nearly triangular ; in labyrinthus there is a 

 deep cavity on the other side of the parietal lamina caused by the 

 whorl descending as it ends before forming the peristome, while in 

 goldmani the whorl does not descend and the area referred to is 

 flattish ; in labyrinthus the short upper lamina is directly opposite 

 the space between the parietal and outer basal laminae, in goldmani 

 the short lamina is opposite the end of the outer basal lamina ; finally 

 the sulcus at the end of the carina in labyrinthus is shallow, wide, 

 and hardly rises above the carina, while in P. goldmani the sulcus 

 is very narrow, recurved, and rises above the carina in a rather large 

 funnel-shaped opening with a thin flaring upwardly directed margin ; 

 this opens into the lumen of the whorl behind the armature of the 

 aperture and may serve the same purpose as the opening behind the 

 aperture in Opistho siphon. 



Maximum breadth of shell 39.0; minimum do. 31.5; height 15.5 

 mm. Similar measurements of an average P. labyrinthus are 50.0, 

 42.0, and 20.0 mm. (See plate 2, figs. 3, 4.) 



PLEKOCHEILUS PIRRIENSIS, new species 

 (Plate i, Figures 1, 2) 

 Shell large, thin, whitish, minutely densely granulose, covered 

 with a rather dark yellow-brown periostracum, painted with narrow 

 oblique zigzag streaks of dark purple-brown, varying in density in 

 different individuals. Nucleus (lost in the specimens) ; whorls about 

 four and a half ; axis barely perforate, the chink overshadowed by 

 the pillar-lip ; peristome white or slightly yellowish, with a thick 

 band of callus uniting the pillar and the outer lip over the body ; 

 throat whitish, the painted pattern showing through, the peristome 

 conspicuously reflected. Dimensions of four specimens : 



A. B. C. D. 



Height of shell 82 83 85 79 



Height of aperture 58 55 55 51 



Maximum diameter of shell 67 55 54 57 



Maximum diameter of aperture 42 38 41 38 



