178 AXEL A. OLSSON 



Pododesmus foUatus (Broderip) Plate 24, figures 3-3d 



Placuanomia foliata Broderip, 1834, Proc. Zool. Soc. London, p. 2. — Reeve, 1859, Conch. 

 Icon., vol. 11, Placuanomia, pi. 1, fig. 5. 



Only the upper or free valve is represented in my collection. These 

 valves may be white or brown, smooth, undulate, or covered with fine 

 radials. According to Broderip's original observation, the shell is attached 

 by its whole lower surface. 



Range — Gulf of California to Peru. Ecuador: Charapota; Isla la Plata; 

 Puerto Callo; Santa Elena. Peru: Lobitos. 



Genus PLACUAIfOMIA Broderip, 1832 

 {Placunomia Swainson, 1840 abridged.) 



Type species by monotypy, Placuanomia cumingii Broderip. 



Shell of moderate size, (height 80 mm.), thick and often strongly 

 plicate, attached by a byssus and by direct cementation of the umbone of the 

 right valve to the substratum, sometimes, later becoming free. Byssal fora- 

 men becomes closed by a vertically layered plug which lies well within the 

 margin of the shell; below it, is placed the single large adductor impression 

 generally surrounded by a whitened area. In the right valve, the ligament 

 is attached to two, large, diverging processes which resemble cardinal teeth 

 and which fit into two deeply grooved sockets in the free valve. Both 

 valves may be deeply plicated over their free zone or irregularly flattened, 

 the surface almost smooth except for growth lines or covered by fine, radial 

 threads. 



Two species distinguished as follows. 



I. Margin of valve with 4 or 5, large, sharp folds or plicae. Surface smooth 

 except for growth incrementals. 



P. cumingii 



II. Margin of valves not sharply folded. Surface with small, threadlike 

 radials. 



P. panamensis 



Placuanomia cnmingril Broderip Plate 24, figrures 1, la 



Placuanomia cumingii Broderip, 1832, Proc. Zool. Soc. London, p. 29 Gulf of Dulce, 

 Costa Rica. — Reeve, 1S59, Conch. Icon., vol. 11, Placuanomia, pi. 1, figs. 3a, 

 3b. — Olsson, 1924, Nautilus, vol. 37, p. 128 (as a Pleistocene fossil in Peru). — 

 Hertlein and Strong, 1946, Zoologica, vol. 31, pt. 2, p. 69. 



Resembles a plicated oyster but fresh specimens have the micaceous- 

 silvery sheen of an Anomia. Shells are quite large, frequently up to 80 mm. 

 in height, subcircular and generally with four or five large, angular plica- 

 tions or ribs. The attachment area varies considerably in size; in some 

 specimens, it may cover more than half of the surface of the lower half 

 while in others, it is hardly noticeable. Except for the large plications and 

 growth incrementals, the surface is smooth. P. plicata Tuomey and Holmes 

 from the Miocene of the Carolinas is similar. The species occurs as a Pleis- 

 tocene fossil in the Lobitos Tablazo at the mouth of Quebrada Parinas, near 

 Talara. It is a widely distributed species along the coast of Ecuador and in 

 all probability extends southward into Peruvian waters. 



Range — Gulf of California to Ecuador. For some records north of Pan- 

 ama see Hertlein and Strong. Ecuador: Palmar near Colonche; Manta; 

 Jaramijo. 



