340 MAZATLAN UNIVALVES 
operculum is on the same plan as in the Cerithia (proper) ; but 
is larger in proportion, thin near the margin, rather concave, 
with the spiral part saucer-shaped, bounded by a raised mar- 
gin; outer surface minutely granulated, more conspicuously 
than in C. maculosum; muscular scar small, with very few 
undulating lines ; remainder of inner surface extremely glossy. 
The smallest adult is 1°14 long ; the largest measures long. 1°45, 
long. spir. 1°5, lat. '5, div. 25°. 
Hab.— Panama; in sandy mud, 2 or 3—7+ fm.; Hinds.— 
Taboga;: very rare; C. B. Adams.—Mazatlan ; common ; 
D’pool & Havre Coll. 
Tablet 1605 contains a series of 5 sp. shewing the formation 
of the adult mouth.—1606, 4 sp. adult, large and small.—1607, 
7 sp. colour varying from light spotted, to uniform brown red.— 
1608, 5 sp. shewing different positions of penultimate varix.— 
1609, 5 sp. with irregularities of growth.—1610, 2 sp. with 
opercula in situ, of which one is abnormal.—1611, 1 sp. with 
operculum cut-off from the dead animal within. It is altogether 
abnormal, irregularly formed of concentric elements, deeply 
indented, and sculptured occasionally with a Y pattern, with- 
out granules. It may be the result of the same injury to the 
shell which fractured the mouth and destroyed the upper 
whirls,—1612, 4 normal opereula. 
390. Vertaaus ———— sp. ind. 
Tablet 1613 contains a fragment, of Cerithiopsoid aspect, but 
with a distinct columellar plait. The whirls are short, numer- 
ous, subquadrate, with two rows of coarse broad tubercles. 
Hab.—Mazatlan ; 1 sp. off Spondylus ; L’pool Col. 
Genus TRIFORIS, Desh. 
Enc. Méth. ii. p. 1053, 1830.— Phol. Handb. Conch. p. 166. — 
H. & A. Ad. Gen. voli. p. 287. 
Cerithium, pars, auct. 
Shel! reversed ; canals sometimes tubular; operculum orbicu- 
lar, few-whirled. This genus appears rare on the W. American 
coast, from which there is not one among the many species 
described by Hinds. Prof. Adams has described three, from a 
few Panama specimens, which are here adopted with great 
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