164 MAZATLAN BIVALVES 
Tablet 735 contains a young elongated specimen. — 736, 
another, rounded form, with a few tubular spines near the mar- 
gin of the upper valve.—737, the largest sp. with Vermetide, Ke. 
215. OstREA ————, sp. ind. | 
P=QOstrea sp. ind. e, C. B. Ad. Pan. Shells, p. 246, no. 384. 
Ostrea iridescens, jun. P. P. C. Cat. Prov. 
Agreeing with O. iridescens in its square form, straight 
hinge, and nacreous interior; differing in the irregular radia- 
tion of the lower valve, and strong sharp plication of the mar- 
gin. This differs from the undulated margin of O. ec. palmula, 
in not having a distinct limb, with remote line of denticles. 
These, if present, are very small, and rather near the margin. 
The characters are so variable that I should have continued to 
regard this as the young of O. iridescens, but for finding 
specimens of the latter without hinge denticles, which in these 
shells are strongly marked ; and for the remark of Prof. Adams, 
with regard to what appears the same species, that the animal 
has a bitter flavour. Long. 2°5, lat. 2°5, alt. 1°35. 
Hab.—Mazatlan; very rare, on shells; ZL’pool Col.—? Pan- 
ama ; very common, attached to rocks and stones from one 
to three-quarters tide level: small var. on Nerita scabri- 
costa; C. B. Adams.—San Diego, Lieut. Green. 
Tablet 738 contains 7 very young valves, off Spondyli and 
Chamex.—739, 1 do. on Imperator olivaceus.—740, 1 do. on 
Imp. unguis, distorting the shell —741, 1 young, white valve, 
resembling O. Virginica, but with crenated hinge.—742, 2 
valves approaching O. iridescens.—743, 4 pairs strongly plicate, 
green within.—744, 1 large pair, attached by portion of the 
valve to Pinna. 
Famity ANOMIAD 4. 
Genus PLACUNANOMIA, Brod. 
Brod. in Proce. Zool. Soc. 1832, p.29.—Gray in B. M. Cat. 
Anom. p. 8. 
Subgenus Monia, Gray, Proc. Zool. Soe. 1849, p. 121. 
216. PLACUNANOMIA PERNOIDES, 7. 8. 
P. t. formé maxime variante, interdum transversda, interdum 
maxime elongata, valvd inferiori maxime perforata, cuneo tntus 
liris haud tenuibus instructo, fulero ligamenti valde extante, 
