A426 MAZATLAN UNIVALVES 
The completion of the peritreme, and absence of the twisted 
columella distinguish this species from Chemnitzia; but no 
plait can be discerned either in the young or old specimen 
which are both quite perfect. A broken specimen would 
probably display it. The species is characterized by the sharp 
ribs, indented at the suture, with the interspaces elegantly 
decussated with curved lines. The young shell, with 4 normal 
whirls, measures Jong. °062, long. spir. °037, lat. °032, div. 30°. 
Adult, with 7 whirls ,, °153, us dD At as, amon. 
Hab.—Mazatlan ; 2 sp. off Spondylus ; Z’pool Col. 
Tablet 1986 contains the adult specimen. 
517. PP CHRYSALLIDA CLAUSILIFORMIS, 7. S. 
2? Chr. t. valde elongatd, effusd, spird “ Clausilie” dextre 
simulante ; vertice nucleoso helicoideo, anfractibus ii. et dimi- 
dio, prominente, verticaliter sito, ab anfractibus normalibus 
separato ; marginibus spire valde excurvatis ; anfr. normalibus 
duobus primis valde tumentibus, via attingentibus ; dein anfr. v. 
subplanatis, suturis expressis, fascia bipartitd, interdum 
subnodulosa ; lirulis obsoletis transversis, et striis spiralibus 
circa basin effusam indistinete ornatd ; totd superficie minutis- 
sime transversim rugulosé ; apertura oblonga, ad basin valde 
effusa ; plicd obliqua, subdeutd ; operculo paucispirali, tenuis- 
simo, rugulis curvatim radiantibus instructo. 
This most aberrant species is placed here from some of its 
characters ; others are so peculiar to itself as almost to justify 
its sectional separation. Its form is that of a dextral Clausilia, 
with the apex of a very acute Chemnitzia, the nearly smooth 
surface of Eulimella, and the fold, the operculum, and the 
constricted mouth of Chrysallida. The peculiarities are the 
separation and tumidity of the first two normal whirls, and the 
structure of the suture. This, instead of being impressed, has 
a slight raised deposit in each whirl, which meets its neigabour 
like the rims of two plates. All the four specimens found were 
imperfect and disintegrating; in one of them however the 
operculum, as well as the vertex, were preserved. The largest 
must have measured when perfect, long. °15, long. spur. *O095, 
lat. 045, div. 20°. 
Hab.—Mazatlan ; 4 sp. off Chama; L’pool Col. 
Tablet 1987 contains the least imperfect specimen, with its 
operculum. 
