MAZATIAN UNIVALVES 431 



B. Wliirls with spiral sculptwe. 

 (a.) Rihs interrupted at the periphery. 



529. Chemnitzia , siJ. ind. (d.) 



Tablet 2000 contains a fragment of a very large, wliite, sub- 

 diaphanous species, with deep grooves between ribs ending at 

 the periphery. The mouth must have been "08 long. 

 ^aZ>.— Mazatlan ; fragment, off Spondylus ; L'pool Col. 



530. Chemnitzia geacillima, oi. s. 



Gh. t. juniore acutisvimd, maxime elongatd ; vertice nucleoso 

 prolongato, marglnibus spires incurvatis ? superante ; anfr. 

 primis solutis,-rotuiidatis ; postea suhplanatis ; costis circ.-Kvi. 

 obtusis, circa penjjheriam suhito truncatis ; hasi rotundata, 

 J(Bvi ; interstitiis spiraliter terme decussatis ; aperturd elongatd ; 

 columelld vix intortd. . 



In most Chemnitzise, even if the spire outlines are nearly 

 parallel in the adult, they are divergent when young. In this, 

 the upper whirls are the sharpest, and scarcely overlap each 

 other. The nucleus appears to have been very large. A worn, 

 dead sp. appears even sharper than that here measured, with 

 fewer ribs. The larger sp. with eight normal whirls, measures 

 long. -117, long. spir. '085, lat. '008— '035, div. 13". 

 JTa5.— Mazatlan ; 2 sp. off Chama ; L'pool Col. 



Tablet 2001 contains the larger specimen. 



(b.) Ribs evanescent at the base. 



531. Chemnitzia tjndata, n. s. 



Ch. t. gracili, tenui, albido-fuscd ; vertice micleoso marginibus 

 spirce subrectls superante ; anfr. (teste juniore) vii. subplanatis, 

 sutwrd profunda ; liris tenuissimis circiter sviii. aculis, vix 

 expressis, circa basin evanidis, interstitiis latis, undatis ; striulis 

 .■^piralibus totam superficiem ornantibus, strid majore circa 

 peripheriam ; labro acuta ; columelld gracili, vix tortd. 



On comparing this shell with the corresponding portion of 

 C. gracilior, C. B. Ad., it is found to have many fewer and 

 much finer and sharper ribs, which do not end at the periphery, 

 like the curved interspaces. Long. '065, long. spir. 'Oi5, 

 lat. -022, div. 14". 

 Sab. — Mazatlan ; 2 young perfect sp. off Spondylus; L'pool CoL 



