PANAMIC-PACIFIC PELECYPODA 147 



Length 36.8 mm., height 23.4 mm., diameter 14.3 mm. 



Venado Beach, Canal Zone. Holotype, ANSP 218932. 



This species is characterized by its relatively small size and large 

 anterior ears. It is named to honor Mr. and Mrs. Lee Beil, formerly stationed 

 in the Canal Zone and whose industrious collecting of Panama shells 

 have added so much to our knowledge of the moUusks of that region. 



Range — Panama. Canal Zone: Venado Beach. 



Genus PDfCTADA Roeding, 1798 

 {Meleagrina Lamarck, 1819) 

 Type species by subsequent designation, Iredale, 1915, Mytilus mar- 

 garitiferus Linne. 



Shell obliquely subrectangular, as high as long, with a long, straight 

 hinge line, wholly posterior of the beak, a small anterior ear, the valves 

 slightly unequal, the right one usually somewhat more convex, attached by 

 a byssus which passes through a notch under the anterior ear. Hinge 

 edentulous, the area covered by the ligament, the resilifer pit is a shallow, 

 submedial depression. Shell made up of two principal layers, an outer, 

 prismatic layer, generally amber or horn-color and forming a wide marginal 

 band, and an inner, shiny, pearly layer. The adductor scar is large, a little 

 posterior of the middle. 



Distinguished principally from Pteria which it much resembles, by its 

 shape, often higher than long, and in the absence of a definite posterior 

 wing. To this genus belongs the pearl oyster of the Bay of Panama. 



Plnctada mazatlanica (Hanley) Plate 18, figures 3-3b 



Meleagrina mazatlanica Hanley, 1856, Cat. Recent Bivalve Shells, p. 388, pi. 24, fig. 40 



(Mazatlan). 

 Avicula barbata Reeve, 1857, Conch. Icon., vol. 10, Avicula, pi. 5, fig. 9 (Panama). 

 Margaritiphora (Pinctata) mazatlanica (Hanley), Maxwell Smith, 1944, Panamic Marine 



Shells, p. 51, fig. 674. 

 Pinctada mazatlanica (Hanley), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 3, 



No. 19, pp. 164, 165.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat Hist., 



vol. 107, art. 2, pp. 175, 176. 



Young shells are relatively thin and delicate but larger specimens become 

 coarse and heavy. Color generally yellowish-olive shading into brown, the 

 surface often worn and encrusted, the middle of the disk showing concentric 

 rings, the edges of growth layers but perfect, unworn shells are covered by 

 close-set, radial spines, usually overlapping and flattened, especially around 

 the margins. 



This is the pearl oyster of the Pearl Islands of the Bay of Panama. 

 Avicula cumingi Reeve, described from the Galapagos, is probably the same 

 species. 



Range — Gulf of California to northern Peru and the Galapagos Islands. 

 Costa Rica: Puntarenas. Panama: Guanico; Panama City; Pearl Islands. 

 Canal Zone: Venado Beach. Ecuador: Santa Elena; Manta. Peru: Paita. 



Family PHILOBETIDAE Bernard, 1897 

 Shell generally quite small, mytiloid or aviculoid in shape, the valves 

 being alike but inequilateral, the anterior side being short or atrophied, 

 attached by a bundle of byssal threads emerging between the anterior mar- 

 gins of the valves below the beaks; monomyarian, the single or posterior 



