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. spur. 1°34, lat. 1°, div. 40°. 
Hab.—San Blas, Kiener.—Gulf of California; in sandy mud ; 
Lieut. Babb.—S. W. Mexico; P. P. C.—Mazatlan ; rare, in 
fine sand; L’pool Col.—(The localities “Gulf Nicoya and 
W. Coast Mexico, Hinds,” assigned to P. olivacea + funiculata 
by Reeve, 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 asp. 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. 
458. PLEUROTOMA MACULOSA, Sow. 
Proc. Zool. Soc. 1833, p. 135.—Rve. Conch. Syst. vol. 1. pl. 233, 
f.8:—Conch. Ic. pl. 6, sp. 45.—Mke. in Zeit. f. Mal. 1851, 
p. 19, no. 89.—(Non P. maculata, C. B. Ad. Contr. Conch. 
no. 4, p. 62. Jamaica.) 
Drillia maculosa, H. & A. Ad. Gen. 1. 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. 1:13, lat. °57, div. 25°. 
