5i20 Zoological Society. 



for one. The first is white, and the two last have a brown blotch 

 on the internal surface of the dorsal valve, 



*** Shell ovate, not plicated ; radiately ribbed. Perforation of 

 lower valve large, only slightly embrachxg the large thin plug. 



MONIA. 



5. Placunanomia macrochisma. 



Upper valve with two scars, partly confluent on the lower hinder 

 edge ; the upper scar largest. Lower valve with an oval oblique scar, 

 narrowed behind, rather in front of the plug. 



Anomia macrochisma, Deshayes, Rev. Soc. Cuvier. 1839, 359 ; 

 Mag. de Zool. 1841, t. 34. 



Placunanomia Broderipii, Gray, B. M. 1842, and Mus. Cuming. 



Hab. Yi.dimi?,c\\Sii\idi; Deshayes. " Onalaski," Mus. Cuming. " Ca- 

 gayan, Lucon," fide " G. B. Soioerby," in Brit. Mus. 



M. Deshayes observes : " On sait que dans le plus grand nombre 

 des Anomies la perforation se reduit ordinaircment en un simple 

 echancrure, parce que les deux parties du bord superieur ne se rejoi- 

 gnent jamais. Ici au contraire le trou est complete, et la valve est 

 reellement perforce." This character is common to all the species of 

 Placunanomia. M. Deshayes does not figui'e nor describe the plug. 

 I think the habitat assigned to this species by Mr. G. B. Sowerby 

 must be a mistake. It is the specimen referred to by Mr. Broderip 

 in the observations on the genus in the Proceedings of the Zoological 

 Society. 



6. Placunanomia cepio. 



Scars 2, far apart ; upper very large, ovate, longitudinal, central ; 

 lower smaller, oblong, oblique, rather behind the upper. 

 Plug large, flat, broad. Notch large, wide. 

 Hab. California; Lady Katharine Wigram ; Brit. Mus. 



7. Placunanomia alope. 



Upper valve flat, smooth, radiately striated. Scars two, well sepa- 

 rated, rounded, equal-sized. 



Hab. California ; Lady Katherine Wigram. 

 Two upper valves in British Museum. 



ff European. 



8. Placunanomia patelliformis. 



Shell suborbicular, convex or quite flat, radiately striated ; inner 

 disk greenish. Apex rather within the dorsal margin. 



The upper muscular scar of the dorsal valve very large, oblong ; 

 the lower one small, roundish, on the lower part of the hinder margin 

 of the upper one. 



The peduncle of the cartilage with a triangular cavity in front, 

 under the tip, and continued in an oblong rib-like ridge towards the 

 centre of the shell. 



Anomia patelhformis, Linn. S. N. 1152; Nov. Act. Vpsal. 1773, 

 i. 42. t. 5. f. 6, 7 ; Retzius, Nov. Gen. Test. ii. ; Sars, fide Mus. Cu- 



