MAZATLAN UNIVALVES 391 



The shells (of which I have examined about 100) scarcely vary, 

 except slightly in acumination. The operculum is formed like 

 an obtuse-angled triangle, with the base along the columella, 

 nucleus near the canal, the other angles rounded ; reddish 

 olive, strong, outside nearly smooth, with the base raised ; 

 muscular scar deeply marked, but not corrugated. The young- 

 est sp. is 1*1 long ; the largest (allowing for the decollation of 

 the spire) measures long. 2 '48, long. spir. 1*34, lat. 1*, div. 40. 

 Hab. San Bias, Kiener. Gulf of California ; in sandy mud ; 

 Lieut. IB abb. S. W. Mexico ; P. P. C. Mazatlan ; rare, in 

 fine sand ; L'pool Col. (The localities "Grulf Nicoya and 

 W. Coast Mexico, Hinds" assigned to P. olivacea + funiculata 

 by Heeve, probably belong to this species. ) 

 Tablet 1879 contains 3 sp. different ages, of which one has 

 the operculum in situ. 1880, the largest sp. with its operculum, 

 mended after fracture ; the original part is from a terminal 

 nucleus, the new third from a central one. The shell has 

 twisted its canal till it is '56 broad, forming a broad false 

 umbilicus. 'Also a sp. incrusted, and with the canal destroyed 

 by sponge ; yet with the operculum in situ. 1881, 2 opercula, 

 one normal, the other with a subcentral nucleus. 



v T~ r 458. PLEUKOTOMA MACULOSA, Sow. 



Proc. Zool. Soc. 1833, p. 135. Rve. Condi. Syst. vol. ii. pi. 233, 

 f. 8 -. Conch. Ic. pi. 6, sp. 45. Mke, in Zeit. f. Mai. 1851, 

 p. 19, no. 89. (Non P. maculata, C. B. Ad. Contr. Conch. 

 no. 4, p. 62. Jamaica.) 

 Drillia maculosa, H. ty A. Ad. Gen. i. 90. 



Shell very constant in form ; thin, slender ; of an ashy 

 colour, more or less spotted or stained with reddish brown ; 

 markings sometimes fine, sometimes in large dashes, sometimes 

 almost wholly absent. Epidermis very thin, smooth, not 

 glossy. First three whirls smooth ; the rest with one row of 

 stout tubercles along the spire, which are rarely coloured ; the 

 whole surface very finely spirally striated. Canal open, too 

 long to rank satisfactorily with Drillia ; labrum smooth, sharp ; 

 posterior sinus large, deep ; anterior slight, open. Operculum 

 closely resembling that of PL funiculata, but longer in propor- 

 tion, with the inner margin scarcely raised. About one in five 

 of the opercula found were abnormal, with the nucleus central. 

 The smallest sp. of 11 whirls, measures '68 ; the largest, (with 

 15 whirls,) long. 1'96, long. spir. 113, lat. '57, div. 25. 



