MAZATLAN UNIVALVES 339 
When adult, the canal is very short, and the labrum slightly 
lirate within. Colour of a prevailing blackish brown, (brown 
in the mouth,) variously dotted and marked with white. The 
operculum is very minutely granular, and closely resembles 
that of C. maculosum on a small scale. It differs from that of 
C. stercus-muscarum in being of a lighter colour, thinner, with 
the spiral part larger in proportion, margin more indented, 
muscular scar smaller, scarcely marked. The smallest specimen 
measures ‘030 by ‘027. The smallest adult, 45 by °2. The 
largest, long. 6, long. spir. °35, lat. 28, div. 30°. This is con- 
siderably larger than Menke’s specimen; but many of Prof. 
Adams’ were an inch long, and of Cer. no. 199, 1°2 long. 
Hab—Mazatlan; rare; L’pool Col.—Taboga and Panama; 
extremely common, on and under rocks and stones, between 
half-tide level, and low water mark of neap tides; C. B. Ad. 
Tablet 1602 contains 3 sp. extremely young, and an adult 
with the operculum.—1603, a series of 7 sp. of different ages.— 
1604, 2 opercula. 
Genus VERTAGUS, Klein. 
HT. & A. Ad. Gen. vol. 1. p. 285. Siphonal canal strongly 
recurved; columella plaited: operculum as in Cerithium, 
(teste V. gemmatus, non teste Ad. fig.) 
389. VerTaaus GEMMaTUs, Hinds. 
Cerithium gemmatum, Hinds, Voy. Sulph. Moll. p. 27, no. 104, 
pl. 11, f.5,6.—C. B. Ad. Pan. Shells, p. 152, no. 197.—Sow. 
Thes. Conch. sp. 17, pl. 177, f. Al. 
Vertagus gemmatus, H. & A. Ad. Gen. i. 285. 
This shell is very constant in its characters; presenting a 
sharp, straight outline, and a sculpture consisting of 3 rows of 
nodules, (of which the upper is the larger,) with a double 
spiral line between. The nodules are but slightly developed 
in the young shell. There are numerous small varical ridges, 
but only two principal ones, at the aperture, and at about two- 
thirds of the last whirl. The siphonal canal in the adolescent 
shell is short, and but slightly recurved: afterwards longer 
and much bent. The posterior canal is thick, but with only a 
slight groove. Theze is no parietal knob distinct from the 
canal, and the columellar plait is very slight and sunken. The 
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