MAZATLAN UNIVALVES 419 
minimis, quarum una suprasuturalis simplex, et iv. tuberculose, 
tuberculis rotundatis, lineis transversis sibt parallelis sitis, in 
anfr. penult. circiter xx., in t. adulta evanidis ; lirulis in basin 
rotundatam erreiter vii., t. juniore acutioribus, interstitiis tenuis- 
sime et creberrime decussatis ; apertura ovata, peritremati viz 
continud ; labro acuto, vie planato, supra suturam producto, ad 
basin vie sinuato ; labio in parietem tenuissimo, infra distincto, 
rimulam umbilicalem formante ; plicd intus acuta, extus obtusa, 
haud conspicud. 
This fine species approaches Monoptygma. . It differs from 
Chr. rotundata in the tuberculation of the spiral ribs and the 
much greater prolongation of the shell. The basal strie seem 
to become broader in the adult, as the tubereulation of the 
upper ribs vanishes. The young shells are slender, with 
rounded bases. ‘The tubercles are arranged in the form of 
transverse ribs, parallel to each other, and running in slanting 
lines to the apex. Joong. °153, long. spir. ‘095, lat. *067, 
div. 22°, 
Hab.—Mazatlan ; 4. sp. and fragment, off Spondylus; Z’pool 
Col. 
Tablet 1971 contains the largest sp. presented by R. D. Dar- 
bishire, Esq. and a very young shell which may belong to this 
species. 
Section B. Species typice. 
507. CHRYSALLIDA communIs, C. B. Ad. 
Chemnitzia communis, C. B. Ad. Pan. Shells, no. 223, pp. 166, 
312. 
Chr. t. ovato-oblongd, gibbosd, solidiore, nitente, alba ; vertice 
nucleoso parvo, spire truncationem dimidio tegente, anfr. i. 
verticaliter sitis, apice via celato; marginibus spire maxime 
excurvatis ; anfr. normalibus iw.—vi, planatis, suturd profunda ; 
clathris transversis, utrinque marginibus spire parallelis, testa 
juniore conspicuis, aperturam versus evanescentibus, juata 
peripheriam terminantibus, anfr. penult. circiter xxii.; liris 
spiralibus iv. vel v. suprasuturalibus, anfr. primis minoribus, 
anfr. ultimis sepe clathras in tubercula secantibus ; lirulis 
rotundatis vix expressis circiter x. supra basin ovatam inter- 
stitus punctulis decussatis ; sculpturd in labro tenuissimo, dia- 
phano evanescente ; labro antice late sinuato, postice planato 
angustato, ad suturam constricto, labio sepe a pariete separato ;. 
