MAZATLAN BIVALVES 149 
Sunarnus MARGARITIPHORA, Meg. 
Megerle v. Mihi feild, 1811.—Meleagrina, Lam. 1819. 
204. MarcaritipHora Mazarnantica, Hanl. 
Meleagrina Mazatlanica, Hanl. Rec. Shells, pl. 24, f. 40. 
No synonyms of the Pearl-oyster are given, as the question 
of the specific identity of the local types is not yet settled. 
The Gulf of California used to be celebrated for its pearl 
fishery, but it appears to have been exhausted, and very few 
oysters have been brought of late years. The specimens from 
S. W. Mexico appeared to belong to the Panama type, being 
small, produced and ofa purplish brown. Of this shell in 1851 
a single vessel brought 340 tons to Liverpool (7. C. Archer.) 
The other local types are the silver-lipped from the Society 
Ts. and the black-lipped from Manilla. Which of these is the 
true M. margaritifera of Lam. has not yet been settled. In 
Hanl. Descr. Cat. are also quoted, p. 264, M. radiata from the 
?W. Indies, and M. albina from Australia. Mr. Nuttall found 
a pretty little species, quite distinct from the young of M. 
margaritifera, at the Sandwich Is. Pearl-oysters are also found 
at Madagascar, Persian Gulf, Ceylon, Swan River, &e. Very 
few specimens were sent in the Mazatlan collection, and of 
these only the young ones were preserved. Shell in that state 
transverse, not produced ventrally, one valve only pierced for 
the byssus, swollen at that part, else flat, spreading; with 
closely set overlapping lamin, extremely thin, produced 
into foliations or flat spines; inside silvery white, nacre bor- 
dered with green, margin broad, of a light tortoisesheli colour. 
Long. 3°55, lat. 4°05, alt. 1°27, (jun.) 
Hab.—Mazatlan ; very rare; L’pool § Havre Coll. 
Tablet 681 contains a very young valve, ‘05 across, of nearly 
normal shape, known from the young of the neighbouring 
species by the enormous size of the prismatic cells.—682, the 
specimen above measured. 
Genus ISOGNOMON, Klein. 
Isognomon, AJein, 1753 :—Dkr. in Moll. Guin. 
Melina, Retz, 1788, Diss. p. 28 :—Sehwm. 1817. 
Perna, Brug. 1792 :—Lam. 1801 :—(non Retz.) 
Sutura, Meg. v. Mihif. 1811. Entw. p. 65. 
