344 PROCEEDINGS OF THE ACADEMY OF [May, 



The embryonic shell, of slightly over 2 whorls, is smooth and 

 projects nipple-like. The following whorls of the cone are strongly 

 ribbed, but the ribs weaken more or less on the cylindrical part, 

 so that on the penultimate whorl they are often inconspicuous or 

 almost wanting (for brevity called "smooth" in the above tables). 

 There is of course complete intergradation in this character, so that 

 the classification in the table is more or less arbitrary. The size 

 averages larger in shells with 2 or 3 lamellae, but there are exceptions. 

 It will be understood that the measurements were based upon shells 

 which to all external appearance are adult or old. After a careful 

 study of the aperture and lip, I think that it may be accepted as 

 certain that the variations in lamellae recorded above are not depend- 

 ent upon age of the individual. 



At Station 10, on the northern slope of Hacheta Grande Mt., 

 a small series was taken. All of them have the whorls of the cylindric 

 portion smooth or nearly so, glossy, the cone and the last whorl, 

 or its last half, being ribbed as usual. Ten specimens opened measure 

 as follows: 



whorls li; axial and basal lamellae. 



" 1 ol . u ii a 1 1 



This lot, by the size of some individuals and the large number 

 (50%) of bilamellate example, is intermediate between crossei and 

 mearnsi, as it also is in the elevation of the station. It has a feature 

 of its own in the smooth median whorls, parallelled, however, by 

 some individuals of crossei from the mountain top. None of the 

 mearnsi seen are so smooth. 



ZONITID^E. 

 Vitrea indentata umbilicata (Ckll). 



Stations 3, 5 and 8. 

 Zonitoides minuscula alachuana (Dall). 



Stations 8 and 11. • 



FERUSSACID.^. 

 Cochlicopa lubrica (Mull). 



Station 8. Scarce. 



