MAZATLAN UNIVALVES 385 



which however it is distinguished by the absence of the lower 

 row of tubercles. There are about 16 whirls, of which the 

 first three are smooth, brown and translucent ; while the next 

 three (about) display the costse without the spiral groove. The 

 young shell is very dark coloured, with the ribs conspicuous ; 

 the girdle gradually develops its white colour, and afterwards 

 very irregular reddish brown spots. The costse gradually 

 become fainter and more irregular, and are or are not decussated 

 by the spiral lines. These are normally 4--6, but variable. 

 The whole surface is covered with microscopic spiral striulse, 

 irregularly waved, giving a rugose appearance. The sutural 

 line is continued round the base in a faint white band. The 

 deeply cut notch is bounded by a sharp keel externally, which 

 runs round over the columella. The colour is almost always 

 purplish brown, shading into olivaceous brown, more or less 

 dark, lustrous. Operculum rhornboidal, more angular than in 

 Pleurotoma, apex at the end of the long diagonal, expanding 

 with straight sides and a scarcely rounded end. Most of the 

 opercula found are abnormal, mended as from a subcentral 

 nucleus. These beautiful shells are often encrusted with black 

 mud, as in Drillia luctuosa, and have frequently been obliged 

 to repair breakages at their extremity. The largest sp., unusu- 

 ally slender, measures long. 1'6, long. spir. 1*2, lot. '34, div. 13. 

 A young broad sp. T06, '74, '28, 19. 



Hob. Mazatlan ; not common ; L'pool Col. 



Tablet 1828 contains 5 sp. usual colour. 18*29, 5 sp. richly 

 olivaceous. 1830, 3 sp. purplish brown predominating. 1831, 

 1 sp. ashy tint, markings faint. 1832, 2 sp. markings very 

 faint. 1833, 3 do. markings very strong. 1834, 3 sp. repaired 

 after simple and compound fractures. 1835, 1 sp. with opercu- 

 lum in situ ; and 2 separate opercula, one normal, the other 

 mended after fracture. 



451. MYUEELLA HINDSII, In. a. 



JLT. t. "_Zfcf. albocinette" simill, sed graciliori ; anfr. confer- 

 tioribus ; omnino albidd, rufo-fusco vix tine t a ; cinqulo aream 

 majorem occupante, tuberculis validis / costis evanidis ; lineis 

 spiralibus iii.-v., striulis haud apparentibus ; plica columellari 

 haud conspicud. 



A very few specimens were found of a whitish colour, faintly 

 spotted with reddish brown ; with the ribs scarcely apparent, 

 and the general surface smooth. Whether the form be of 

 Nov. 1856. JcJc 



