394 MAZATLAN UNIVALVES 



name was pre-occupied by Sow. The inaccuracy of the figure 

 in the Conch. Ic. and the variation in the number of spiral 

 tubercular striae (in this species not a constant character,) excuse 

 Menke for having redescribed it. The P. atrior of Prof. 

 Adams, described from a single specimen, appears to be char- 

 acterized by the pale spiral stripe ; which, though rarely con- 

 spicuous, and not noticed in the diagnosis of the species, may 

 generally be seen inside the mouth, by holding the shell up to 

 the light ; and in fine specimens is often clearly discernible on 

 the last whirl. The P. discors scarcely differs in essential 

 characters, though it is a much larger form. Shell with the 

 entire surface very minutely spirally striated; with a prominent 

 keel near but not close to the suture, which partially covers 

 the principal row of nodules, 12 14. Below are several spiral 

 lirulse of which generally two, sometimes more, are prominent 

 and granular, the granules corresponding with the tubercles 

 above. Sinus rather narrow and deep, in the middle of a large 

 excavated area ; with the thick posterior callosity labral rather 

 than parietal. A narrow horn-coloured band, sub -transparent, 

 runs just above the tubercles ; (in one specimen broad, cover- 

 ing the tubercles, = P. atrior, C. J5. Ad.) Operculurn broader 

 than in D. luctuosa, of a deep rich purplish red colour, very- 

 glossy inside. The spire outlines are very convex in the adult, 

 which has somewhat the aspect of a small D. rudis. The small- 

 est adult sp. (decollated) measures '34 by '15. The longest, 

 long. '72, long, spir*. '36, lat.'VA, div. 35. (anfr. sup.) 

 The broadest sp. measures lat. '28, div. 40. 

 Hob. Monte Christi ; under stones, Cuming. Panama ; 



14 sp. do. at low water mark ; C. B. Adams. Mazatlan ; 



not common, often incrusted with coralline, very rarely with 



mud ; L'pool Col. 



Tablet 1891 contains 8 specimens, different ages. 1892, 4sp. 

 spire more elevated. 1893, 3 sp. acuminated ; sculpture some- 

 times nearly obsolete. 1894, 3 sp. dwarf state. 1895, 2 sp. 

 light band developed. 1896, 2 sp. with opercula, one normal, 

 ' the other with nucleus subcentral ; and one separate operculum. 



462. ?DEILLIA CEEITHOIDEA, n. s. 



?D. t."D. aterrimce" simili; sed carince infrasuturali carente, 

 (inter 'dum stria majore Me monstrantej area sinus angustiore, 

 hand excavata, superiors ; monilibus spiralibus in basipluribus ; 

 tuberculis in spird magis conspicuis ; labro serrato, sinu pro~ 



