4\A, MAZATLAN UNIVALVES 
transversis, valde extantibus, ad basin continuis ; interstitiis 
subundulatis, levibus ; apertura elongatéd, peritrematt con- 
tinud, axt plick distinctad muntté. 
Nuclear part very small and sunken ; next whirl with 
numerous, fine, rather undulating ribs; which gradually be- 
come sess numerous, straight, sharp, and very prominent. 
.Whirls sharply angled at the shoulder, at rather less than 90°. 
The lip is breken in both specimens, but it is distinctly con- 
tinuous. There is a general resemblance in form, (though the 
whirls are less numerous and longer) to Chemnitzia scalaris. 
Long. ‘1, long. spir. ‘065, lat. °37, div. 20°. 
Hab.—Mazatlan ; 2 sp. off Chama; L’pool Col. 
Tablet 1962 contains the finest specimen. 
498. PARTHENIA QUINQUECINCTA, 72. 8. 
P. t. formé “ P. scalariformi” stinulante ; sed vertice nucleose 
tumente, anfr. ii., verticaliter sitis ; anfractibus 11. et dimidio 
planatis, equaliter transversim clathratis ; clathris acutis cir- 
citer xill. ad suturam antice declivibus, postice muricatis 3 
suturis acute exaratis ; lirulis v. spiralibus cinctd, quarum una 
‘suturam continuat, altera supra partem declivem, tres in basi 
site sunt: apertura ovali, peritremati continua, plict parva, 
declivi, intus celata, haud umbilicata. 
The first normal whirl of this beautiful shell is marked like 
the rest. The ribs are more numerous than in P. scalariformis, 
from which it is at once distinguished by the 5 spiral threads, 
of which 3 appear on the base, one carries on the suture, and 
the fifth is above it, bounding the slanting portion of the 
whirls. Long. °063, long. spir. °038, lat. °025, div. 20°. 
Hab.—Mazatlan ; 2 sp. off Spondylus; L’pool Col. 
Tablet 1963 contains the finest specimen. 
499. PaARTHENIA LACUNATA, 7%. S. 
P. t. ovali, minimé, albd, tenwi, subdiaphand ; vertice 
nucleoso marginibus spire subexcurvatis nequaquam superante, 
decliviter sito, rotundato, viz tumente, apice celato; anfr. i. 
normalibus clathris circiter xviii. solidis tranversis obtusis, munt= 
tis ; peripheriam versus & lacuna concava, insculpta interruptis, 
circa basin ad umbilicum minimum tenue continuis; lacund 
carinis duabus spiralibus cinctad, quarum una supra suturam, 
una ad suturam site sunt; interstitiis ad basin tenuissime 
