416 MAZATLAN UNIVALVES 
ornata, quarum prima ultinam anfractus superioris tegit ; 
carina quarté in basin angulatam sitéd ; apertura ovali ; labre 
solido ; plicd parva, celata. 
This stout little shell is at once recognized by its strong 
keels, of which two appear on the penultimate whirl, the third 
being covered by the first of the ultimate. Long. 252, long. 
spur. °03, lat. ‘032, div. 35°. 
Hab.—Mazatlan ; 2 sp. off Chama; L’pool Col. 
Tablet 1966 contains the largest specimen. 
502. PARTHENIA ZIZIPHINA, 7. s. 
P. t. conicd, alba ; vertice nucleoso mammillato ; anfr. liris 
rotundatis v. spiralibus, quarum una major ad peripheriam, 
due in spird, due in basi angulata site sunt; plicd transversd. 
Tablet 1967 contains a small Ziziphinus-shaped shell, very 
young, differing from P. exarata in the number and strength 
of the spiral ridges. Long. ‘026, lat. *022. 
Hab.—Mazatlan ; 1 sp. on Chama; L’pool Col. 
Suspcenus CHRYSALLIDA. 
Testa utrinque constricta, pupiformis ; peritrema continuum, 
ad basin undatum ; labrum juxta aperturam tenue, intus soli- 
dius ; plica columellaris declivis, sepe celata ; superficies ple- 
rumque cancellata. Operculum | sp. typ.| radiatim corrugatum. 
Chemnitzia, pars, C. B. Adams, (Pan. Shells, no. ?220, ?222, 
223, 226.) . 
The typical species differ from Chemnitzia in having a dis- 
tinct, though hidden plait; from Odostomia proper in having 
the peritreme continuous ; from Monoptygma in the Pupiform 
growth, contracted at each end; and from all in the labrum, 
which is extremely thin at the edge, in the adult as well as in 
the young shell ; while within, as shewn by broken specimens, 
it is tolerably strong. That the sectional limits are not exactly 
defined, is true of almost every group in this family. Similar 
forms. occur both in the E. and W. Indies. The Mazatlan 
shells are represented by 15 species, of which about 650 speci- 
mens were found. The specific characters often depend on 
very minute differences. 
