MAZATLAN UNIVALVES 483 
seu varius virescente ; swperne conspicue angulato, carind tuber- 
culosd ; tuberculis plerumque viii. compressis, plus minusve 
conspicuis, costis radiantibus, sepe subobsoletis, convenientibus ; 
lirulis spiralibus confertis, supra carinam minus conspicuis, 
yotundatis, squamosis cinctd, quarum interdum iui. infra carinam 
majores, quasi carinule, sguamis majoribus tuberculis conveni- 
entibus ; squamulis lirularum confertissimis, acutioribus, arcua- 
tis, labrum acutum crenulantibus ; labio simplici, haud extante ; 
canali elongatd, apertd; costa plus minusve contortd, rimam 
umbilicalem sepe formante : operculo pyriformi, arcuato, nigro- 
rufescente ; margine tenui, diaphano, intus rubro tincto ; cicatr. 
muse. lineis incrementi paucis irregulariter concentricis. 
The figures of Blainv. and Kien., drawn from a supposed 
unique specimen, represent the usual state of this pretty little 
species much better than that of Reeve which (if the same 
species) is an aberrant form.* ‘The shell varies extremely in 
shape and strength of sculpture, but presents a general lozenge 
outline from the keel which is always conspicuous. Whether 
the secondary keels are developed on the basal part of the whirl, 
depends on the individual, and is rarely the case in young shells. 
Almost all the numerous specimens were copiously encrusted 
with coralline, so that the beautiful markings are rarely seen 
except near the mouth. The largest of the specimens mea- 
sures long. 1°28, long. spir. °6, lat. *88, div. 60°. 
Ayoungacuminated sp. °78, - “B2, 5, ° 47, eens 
A depressed sp. ae St Oot As 52D ABW aerOne 
Hab.—Mazatlan, Botta.—(P. diadema) Payta; on the reefs: 
Cuming. —Mazatlan ; common; L’pool Col. 
Tablet 2262 contains 6 sp. basal keels developed, spire ele- 
vated.—2263, 5 do, less elevated.—2264, 5 do. depressed.—2265, 
5 do. basal keels scarcely marked.—2266, 5 sp. base plain, much 
depressed.— 2267, 6 do. less depressed. — 2268, 4 do. acumi- 
nated.—2269, 6 sp. shewing the lip in different stages of growth. 
—2270, 3 do. mouth highly coloured.—2271, 1 do. canal twice 
formed.—2272, 2 sp. much inerusted.—2273, 3 sp. adhesions 
incommoding the mouth.—2274, 4 sp. mended after fracture.— 
2275, 1 sp. curiously worm-eaten.—2276, 8 normal opercula.— 
2277, 4. do. somewhat irregular ; one with nucleus subcentral. 
* Perhaps the tickets of the types in Mus. Cuming have been displaced. 
"Reeve gives the shell as 8. American: but the ‘‘Cuma diadema, Zam.” of the 
collection is ticketed ‘‘ Mauritius,” and is certainly distinct from the Mazatlan 
shell. The latter more nearly resembles C. calcar, Brod, in the collection, 
