MAZATLAN TTNIVALVES 369 



This shell closely resembles Ckrysallida nodosa in form and 

 sculpture ; but although the specimens were broken, there is 

 no indication of columellar fold ; what remains also of the apex 

 accords better with Alaba than with that genus. The char- 

 acter of the mouth comes nearest to A. sapralirata. Long. "08, 

 long.spir. "044, lat. 'OoG, div. 50". 

 Hah. — Mazatlan ; 4 sp. off Spondylus ; L'pool Col. 



Tablet 1728 contains the most characteristic specimen, though 

 another retains rather more of the apex. 



431. PAlaba mutans, nom. prov. 



A. t. ovoided, alba ; vertice parvo, declivi ; anfr. ii. sequenti- 

 hus tumentihus, Icevihus ; dein anjractu uno minus tumente, 

 snperjicie tran^versim minutissime rugulosd, interdum costis 

 ohsoletis transversis ; dein anfractihus normalihus ii., Uris 

 validis spiralihus cinctis, (in anfr. penult. x.J interstitiis rugulis 

 minutissimis transversim ornatis, costis quoque transversis, paene 

 ohsoletis, aperturam versus evanidis ; hasi rotundata ; aperturd 

 ovali, ad basin effusd ; rimuld umbilicali ornatd ; peritremati 

 continuo ; labro a lirulis indentato, lahio tenui ; columelld haud 

 plicatd. 



The shell, in its disparity of whirls, and in the minute 

 transrerse rugulation of its surface resembles PChrysallida 

 clausiliformis ; in its ovoid form, the more tj-pical Chrysallidse ; 

 from -which it differs in the entire absence of columellar plait, 

 as an otherwise unfortunate breakage on the spire clearly 

 proves. It may be a E-issoid, and resembles in many respects 

 PLitiopa saxicola, G. B. Ad. Pan. Shells, p. 183, no. 256, (which 

 Dr. Gould assigns to Ciugula, not having any columellar trun- 

 cation, and on the labruui of whicli, in Mr. Cuming's specimens, 

 there is no deposit, but a continuous peritreme, with an umbili- 

 cal chink.) Long. 'OSS, long. spir. -018, lat. "OIG, div. 33^ 



Sab. — Mazatlan ; 1 sp. oflf Spondylus ; L'pool Col. 



Tablet 1729 contains the specimen. 



432. PAlaba laguncula, nom. prov. 



?A^ t. elongatd, alho-fuscd ; vertice tumentiore, declivi ; anfr. 

 iv. priniis Icevihus, suhplanatis, suturis canaliparvd, impressd 

 instructis, marginibus spirts valde excurvatis ; dein suhito Uris 

 spiralihus validis, rotundatis, extantibus ; interstitiis parvis, 

 decussatis ; 



