PANAMIC-PACIFIC PELECYPODA 87 



4. Shell thinner, inequivalve, with discrepant sculpture. Cardinal area 

 smooth or with the ligamental groove sparingly developed. 



Subgenus Cunearca 



II. Cardinal area usually not fully covered by the ligament, the anterior 

 portion wholly or partly bare (in some species, the ligamental grooves 

 encroach more widely in large, gerontic specimens). 



C. Cardinal area elongate or narrowly subtrigonal, much longer than high. 

 Shell elongated or subelliptical in shape. 



5. Posterior side not winged or deeply emarginated. 



5a. Shell inequivalve, thin, fluted within, the ribs simple, smooth or weakly 

 noded. 



Subgenus Scapharca 

 Not regional. 



5b. Shell equivalve, solid, the ribs generally mesially grooved in the adult. 



Subgenus Sectiarca, new subgenus 



6. Posterior side winged or deeply emarginated, the ribs plain or noded. 



Subgenus Caloosarca, new subgenus 



D. Cardinal area subtrigonal, high. Shell subovate, elevated, inflated and 

 often quite thin. Ribs plain or noded, separated by flat interspaces. 



Subgenus Esmerarca, new subgenus 



Subgenus DILUYARCA Woodring, 1925 



Type species by original designation, Area diluvii Lamarck. Miocene, 

 Europe. 



Shell subequivalved, the margins closed, moderately solid. Cardinal 

 area long and relatively narrow, covered by the ligament on both sides 

 of the beak and deeply engraved with crowded transverse or chevron- 

 shaped grooves. Sculpture more or less similar in the two valves and 

 formed by numerous rounded smooth or coarsely noded ribs. Periostracum 

 coarse and of a dark color. 



Diluvarca was proposed by Woodring in 1925 as a subgenus of Barhatia 

 and believed to differ from Anadara in having a closed ventral margin. 

 The weakly sinuated margin shown by Linnean type of Anadara antiquata 

 is probably due to wear and not a natural byssal gap. Nevertheless, typical 

 Anadara as defined in the key does not seem to occur in our American 

 Tertiary and Recent faunas. For the American species, most clearly related 

 to Anadara, sensu stricto, the name "Diluvarca" will be used. 



4nadara (Diluvarca) tuberculosa (Sowerby) Plate 7, figures 3, 3a 



Area tuberculosa Sowerby, 1833, Proc. Zool. Soc. London, p. 19 Real Llejos, Nicaragua; 



mangrove roots. — Reeve, 1844, Conch. Icon., vol. 2, Area, pi. 3, fig. 18. 

 Area (Seapharca) tubereulosa Sowerby, Dall, 1910, Proc. U. S. Nat. Museum, vol. 37, 



No. 1704, pp. 154, 253, pi. 27, fig. 4. 

 Scapharca (Scapharca) tuberculosa (Sowerby), Maury, 1922, Paleont. Amer., vol. 1, 



No. 4, pp. 26, 27, pi. 1, fig. 12. 

 Anadara (Anadara) tuberculosa (Sowerby), Reinhart, 1943, Special Paper, Geol. Soc. 



America, No. 47, p. 63. — Rost, 1955, Allan Hancock Pacific Expeditions, vol. 



20, no. 2, p. 195, pi. 13, figs. 17 a-b. 



Shell obliquely ovate, rather solid, broadly convex, slightly more so 

 along the posterior-umbonal slope, equivalve. When living, the shell is 



