MAZATLAN UNIVALVES 331 
and changing to another. The adolescent portion is generally 
swollen, of smoother growth; the adult with the whirls irregu- 
lar, more or less drawn out, and frequently with sharp ridges 
of growth behind the labrum. But whatever condition the 
adult may assume, the young shell always has one sharp spiral 
keel in the middle of each whirl, surrounded by spiral strie. 
The operculum is of uniform colour, with about 18 whirls ; 
with one row of sharp tubercular hairs next the suture, and 
other more stumpy ones following; with a very fine border, 
radiately striated, followed by a long hairy fringe. The 
youngest sp. has five whirls, of which the first two are smooth. 
It measures ‘048 by ‘028. An adolescent specimen (12 whirls) 
measures long. 2°07, long. spir. 1°64, lat. *74, div. 22°. 
The largest (17 whirls) 4°5, Bs 3°88. 98. 222 lOne 
A slender sp. (15 whirls) 3°7, __,, 3 Zhe ss gk Cont ieomeeelee 
Hab.—Acapulco, Humboldt & Bonpland.—Panama, Kiener.— 
Payta, Salango, Guacomayo ; in sandy mud, 5—10 fm. ; 
Cuming.—S. W. Mexico, P. P. C—Mazatlan ; not uncom- 
mon; pool Col. 
Tablet 1552 contains 6 sp. extremely young.—1553, 2 sp. 
young; one passing from chalcedony to purple brown, then 
suddenly to nearly white, then gradually to dark, lmnear 
pattern. 
(1.) Tablet 1554 contains 2 sp. uniform purple black; one, 
whirls flat, the other rounded.—1555, 2, sp. very dark, tinted 
with orange brown.— 1556, 2 sp. black purple ground, slightly 
variegated with white.—1557, 3 do. normal state, with more 
white; one has passed through acid, to display colour.—1558, 
3 do. purple, light abounding; one in cashes above, clouded 
below ; another with both large and small pattern.—1559, 3 do. 
light predominating; brownish purple in clouds, dashes or 
spots. 
(2.) Tablet 1560 contains 3 sp. dark olive brown, with purple, 
linear pattern or variegated.—1561, 2 do. white abounding.— 
1562, 3 do. light tint, linear markings conspicuous. 
(3.) Tablet 1563 contains 1 sp. purple brown passing into 
orange brown.—1564, 2 sp. nearly uniferm orange brown; one 
nearly smooth, with blunt shoulder keel; the other rough, 
keeled above and below.—1565, 3 do. with faint purple brown 
cloudings; one very slender, lower whirls separating.—1566, 
2 do. lower whirls passing into normal colouring.—1567, 2 do. 
upper half of the whirls richly variegated.—1568, 3 do. light 
predominating ; pattern clouded or dotted. 
