MAZATLAN BIVALVES 89 
121, 6. CHAMA P FRONDOSA: va7’. FORNICATA. 
C. ?frondosa, t. costis numerosis irregularibus radiantibus, 
squamis fornicatis crebris indutis ; huc et illuc frondosd ; intus 
alba, ad marginem rubro-purpured ; margine crenulato ; den- 
tibus ad apicem valde serratis ; epidermide cinerea ; per totum 
latus affixd. 
Compare C. Buddiana, C. B. Ad. Pan. Shells, p. 253, no. 405 ; 
Panama, rare ; Guaymas, Lieut. Green. 
A few specimens differed from the rest of the Mazatlan 
Chame in having the surface (especially anteriorly) covered 
with radiating coste, rising into scales which are often semi- 
tubular. The colour never displays the rich purple and orange 
of C. frond. Mexicana, being white bordered with puce. The 
attachment is more completely lateral ; margins more strongly 
crenate; edge of hinge tooth sharply serrate. Shell covered 
with an ashy epidermis, sometimes olivaceous, not noticed 
even in young specimens of C. frond. Mexicana. These charac- 
ters might be sufficient to mark out a species, if constant: but 
as I find many of the adult specimens that cannot be referred 
- with certainty to either form; and as each of the characters 
(except that of the epidermis) is in both forms subject. to vari- 
ation, their claim cannot be regarded as established. The 
shell seems to have relations both with C. Broderipu and C. 
Buddiana: on the other hand it sometimes displays posteriorly 
more of the characters of C. frondosa proper than does the 
ordinary form. The valves unite so closely that a specimen 
(attached to Byssoarca) on being opened, two years after being 
brought to this country, was found full of the soft animal mat- 
ter, of course in a state of the most fetid decomposition. In 
the young state it is not to be distinguished from C. frond. 
Mexicana, and scarcely from C. spinosa. It is also of the 
same size and habit of growth. 
Hab.— Mazatlan ; very rare; L’pool Col. 
Tablet 439 contains 2 pairs and a valve, very young.—440, a 
pair young.—441 a pair well formed, adhering to the inside of 
a very large valve. The latter is incrusted with Sponge, Ver- 
metide, &c., and nestled beneath the umbo two specimens of 
Byssoareca gradata have found a home. 442, a sp. attached to 
living Byssoarca ipacifica (v. supra).—443, a large specimen, 
containing i in the upper valve Petricola robusta.) in situ; in the 
lower, which had been attached to ? rock by a large surface, 
