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 Vermetidse, &c. 



215. OSTKEA , sp. ind. 



? = Ostrea 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. c. 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 ; aAd 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. 

 Hob. Mazatlan ; very rare, on shells ; Lpool 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 

 Chamse. 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. 



FAMILY ANOMIAD^. 

 GENUS PLACUNANOMIA, Brod* 



Brod. in Proc. Zool. Soc. 1832, p. 29 Gray in B. M. Cat. 



Anom. p. 8. 

 Subgenus Monia, Gray, Proc. Zool. Soc. 1849, p. 121. 



216. PLACCJNANOMIA PEENOIDES, n. s. 



P. t. forma maxime variante, inter dum transversa, inter dum 

 maxime elongatd, valvd inferiori maxime perf or atd, cuneo intus 

 liris hand tenuibus instructo, fulcro ligamenti valde extante, 



