MAZATLAN UNIVALVES 369 



This shell closely resembles Chrysallida 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. supralirata. Long. '08, 

 long. spir. '044, lat. '056, div. 50. 

 Hob. Mazatlan ; 4 sp. off Spondylus ; Upool Col. 



Tablet 1728 contains the most characteristic specimen, though 

 another retains rather more of the apex. 



481. ? ALABA MUTANS, nom. prov. 



A. t. ovoided, alba ; vertice parvo, dcclivi ; anfr. ii. sequenii- 

 bus tumentibus, lavibus ; dein anjractu uno minus tumente, 

 superficie transversim minutissime rugulosd, interdum costis 

 obsoletis transversis ; dein anfractibus normalibus ii., liris 

 validis spiralibus cine t is, (in anfr. penult, x .) interstitiis rugulis 

 minutissimis transversim ornatis, costis quoque transversis, pcene 

 obsoletis, aperturam versus evanidis ; bast rotundatd ; aperturd 

 ovali, ad basin effusd ; rimuld umbilicali ornatd ; peritremati 

 continue ; labro a lirulis indentato, labio tenui ; columelld haud 

 plicatd. 



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

 transverse rugulation of its surface resembles ? Chrysallida 

 clausiliformis ; in its ovoid form, the more typical Chrysallidae ; 

 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 Eissoid, and resembles in ma*ny respects 

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

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

 cation, and on the labrum of which, in Mr. Cuming's specimens, 

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

 cal chink.) Long. 'Q88, long. spir. '048, lat. '046, div. 33. 

 Sab. Mazatlan ; 1 sp. off Spondylus ; L'pool Col. 



Tablet 1729 contains the specimen. 



432. ?ALABA LAGUNCULA, nom. prov. 



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

 iv. primis Icevibus, subplanatis, suturis canali parvd, impressd 

 instructis, marginibus spires valde excurvatis ; dein subito liris 

 spiralibus validis, rotundatis, extantibus ; interstitiis parvis, 

 decussatis ; 



