MAZATLAN UNIVALVES 429 



profunde excavatis ; basi Icevi, rotundatd ; labro tenui ; colu- 

 mellCi eleganter inflexd. 



This beautiful little species closely resembles Ch. turrita, 

 C. B> Ad. Pan Shells, no. 230, pp. 169, 312 ; from which it 

 differs in the entire absence of spiral keels at the base. The 

 apical whirls are extremely tumid ; the rest are all flat, com- 

 pact, and somewhat muricated at the sutures by the projecting 

 ribs. Long. '09, long. spir. '07, lat, "027, div. 13. 

 Hob. Mazatlan ; 5 sp. off Spondylus ; Epool Col. 



Tablet 1993 contains 2 sp. differing in texture, and in the 

 position of the apex, but probably conspecific. 



(b .) Itibs more or less continuous over the base. 



523. CHEMNITZIA PAFFINIS, C. B. Ad. 



Pan. Shells, no. 221, pp. 165, 311. 



Although this species is described as "very smooth ante- 

 riorly," the type specimen in Mr. Cuming's collection is 

 distinctly striated spirally round the base, over which there is 

 a very faint indication of the ribs : apex scarcely projecting, 

 of two whirls. The Mazatlan specimen is rubbed ; it has 

 seven whirls and measures long. '068, lat. *03, div. 20. 

 Sab. Panama ; 2 sp. in the sand ; C. J5. Adams. ? Mazatlan ; 



1 sp. off Chama ; L'pool Col. 



Tablet 1994 contains the specimen. 



524. CHEMNITZIA PROLONGATA, n. s. 



Ch. t. elongatd, gracili, tereti, albidd ; vertice nucleoso anfr. ii. 

 helicoideis, marginibus spires subrectis haud superante ; anfr. 

 normalibus xi. subconvexis, suturis impressis ; costis subacutis 

 circiter xxii., haud continuis, vix declivibus, ad basin tenue 

 prolongatis, ad rimulam umbilicalem ascendentibus ; aper- 

 turd ovatd ; labro acuto ; columelld eleganter intortd. 



This graceful species, a little group of which was discovered 

 in a cavity on Spondylus by Mr. Darbishire, is distinguished 

 from similar West coast species by the faint prolongation of 

 the rather slender ribs over the base to the umbilical chink 

 formed by the slight twisting of the columella. The nuclear 

 vertex is not broader than the next whirl. An adult specimen 

 measures long. *215, long. spir. *175, lat. "05, div. 13. 



