318 MAZATLAN UNIVALVES 



other seas ; these, from the sponge of commerce, and from the 

 Isle of France (Beau) appear distinct ; those from "Singapore" 

 (among Chams and Plicatnlse,, P. P. C.) offer no grounds of 

 specific separation. I have not however ventured to insert 

 them in the habitat, as a larger series of perfect shells may 

 shew distinctive characters. From Mazatlan traces were found 

 (including varieties) of 51 specimens, of which about 20 were 

 perfect, and 4 possessed their opercula. 



The smallest measures long. '04>7, lat. '017. 



The longest ., „ -145, „ 'OlS— -025. 



The largest „ „ 'M, „ -02 —-032. 



^«5. — Mazatlan ; very rare, off Chamse, Spondyli, &c. ; 



L'pool Col. 



Tablet 1518 contains 7 specimens varying in age and sculp- 

 ture, with a fragment having C. firmatum interwedged.— 1519, 

 1 fresh sp. with operculum ; ribs close and deeply chiseled. 



Var. TENUiiiEATUM ; t. liris crehris, fenuibus ; apice parum 

 prominenti. Tablet 1520 contains 1 specimen. 



Var. sxJBOBSOLETFii ; t. alba, alabastro simili / liris paucis 

 interdum inx momtrantibus. Tablet 1521 contains a young 

 and an adult specimen. 



Var. STTBCON ICTTM ; t. sepfo maxime elevato, subconico. Tablet 

 1522 contains a perfect, and a worn specimen. The latter 

 appears to have its apex subcentral, and may be distinct. The 

 value of the several distinctions above named cannot be tested 

 till more specimens are procui'ed. 



Among all the specimens of Mazatlan Caeca, only one was 

 found with its spiral apex. It was so extremely frail that (not 

 however until after careful observation) it dropped ofi'on touch- 

 ing with a camel hair pencil. This portion possessed two whirls, 

 of somewhat irregular flattened growth, differing in texture 

 from Vitrinella, and much smaller, measuring only '006 by "OOl. 

 About half a -nhivl however remained on the shell, separated 

 from the normal part by a very distinct suture. On removing 

 this, it was found that no plug had yet been formed. The 

 species is therefore indeterminate, as the shell is in the main 

 smooth, with extremely faint traces both of concentric and long- 

 itudinal sculpture. It is placed provisionally under C^ lirato- 

 cinctum. The normal part measures lo)ig. '028, lat. 'OOiS— "009. 



Tablet 1523 contains the specimen. 



