MAZATLAN BIVALVES 89 



J_ 121, b. CHAMA ? FBONDOSA : var. FOBNICATA. 



C. ?f rondos a, I. costis numerosis irregularibus radiantibus, 

 squamis fornicatis crebris indutis ; hue et illucf rondos a ; intus 

 alba, ad marginem rubro-purpurea ; margine crenulato ; den- 

 tibus ad apicem valde serratis ; epidermide cinered ; 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 

 Chamae in having the surface (especially anteriorly) covered 

 with radiating costae, rising into scales which are often semi- 

 tubular. The colour never displays the rich purjple 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 cann6*t be regarded as established. The 

 shell seems to have relations both with C. Broderipii 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. spinoga. It is also of the 

 same size and habit of growth. 

 Hob. 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- 

 metidae, &c., and nestled beneath the umbo two specimens of 

 Byssoarca gradata have found a home. 442, a sp. attached to 

 living Byssoarca jpacifica (v. supra). 443, a large specimen, 

 containing in the upper valve Petricola robusta in situ ; in the 

 lower, which had been attached to ? rock by a large surface, 



