MAZATLAN UNIVALVES 431 
B. Whirls with spiral sculpture. 
(a.) Ribs interrupted at the periphery. 
529. CHEMNITZzIA ————, sp. ind. (d.) 
Tablet 2000 contains a fragment of a very large, white, sub- 
diaphanous species, with deep grooves between ribs ending at 
the periphery. The mouth must have been ‘08 long. 
Hab.—Mazatlan ; fragment, off Spondylus ; L’pool Col. 
530. CHEMNITZIA GRACILLIMA, 2. S. 
Ch. t. juniore acutisstmd, maxime elongatéd ; vertice nucleoso 
prolongato, marginibus spire incurvatis ? superante ; anfr. 
primis solutis, rotundatis ; postea subplanatis ; costis cire. xvi. 
obtusis, circa peripheriam subito truncatis; basi rotundata, 
levi; interstitis spiraliter tenue decussatis ; apertura elongaté ; 
columella vie intortd. 
In most Chemnitzie, even if the spire outlines are nearly 
parallel in the adult, they are divergent when young. In this, 
the upper whirls are the sharpest, and scarcely overlap each 
other. The nucleus appears to have been very large. A worn, 
dead sp. appears even sharper than that here measured, with 
fewer ribs. The larger sp. with eight normal whirls, measures 
long. *117, long. spir. *085, lat. *OO8— *035, div. 13°. 
Hab.—Mazatlan ; 2 sp. off Chama; L’pool Col. 
Tablet 2001 contains the larger specimen. 
(b.) Ribs evanescent at the base. 
531. CHEMNITZIA UNDATA, 2. 5. 
Ch. t. gracili, tenui, albido-fused ; vertice nucleoso marginibus 
spire subrectis superante ; anfr. (teste juniore) vii. subplanatis, 
suturd profunda ; liris tenuissimis circiter xviii. acutis, via 
expressis, circa basin evanidis, interstitiis latis, undatis ; striulis 
spiralibus totam superficiem ornantibus, strid majore circa 
peripheriam ; labro acuto ; columella gracili, vix torta. 
On comparing this shell with the corresponding portion of 
C. gracilior, C. B. Ad., it is found to have many fewer and 
much finer and sharper ribs, which do not end at the periphery, 
like the curved interspaces. Long. ‘065, long. spir. *045, 
lat. ‘022, div. 14°. 
Hab.—Mazatlan ; 2 young perfect sp. off Spondylus; L’pool Ooi. 
