PANAMIC-PACIFIC PELECYPODA 273 



Generally larger than Macrocallista, s.s. and with a more ovate or 

 circular shape. Hinge heavy, the left anterior lateral tooth large. Surface 

 smooth on the adult portion, the umbones with stronger, well-spaced con- 

 centrics {Callista-\\\iQ). 



Aside from shape and possibly a stronger hinge, the differences between 

 Macrocallista, s.s. and Megapitaria are trivial and hardly above specific 

 value. 



Subgenus MACROCALLISTA, s.s. 



Macrocallista (.Macrocallista) squallda (Sowerby) Plate 46, figures 2-2c 



Cytherea squolida Sowerby, 1835, Proc. Zool. Soc. London, p. 23. — Sowerby, 1851, Thes. 



Conch., vol. 2, Cytherea, p. 629, pi. 131, figs. 87, 88, 89. 

 Dione squalida (Sowerby) Reeve, 1863, Conch. Icon., vol. 14, Dione, pi. 3, fig. 10. 

 Macrocallista (Chionella) squalida squalida (Sowerby), Maxwell Smith, 1944, Panamic 



Marine Shells, p. 59, fig. 757. 

 Megapitaria squalida (Sowerby) Hertlein and Strong, 1948, Zoologica, vol. 33, pt. 4, p. 



168.— Hertlein and Strong, 1955, Bull. Amer. Mus. Nat. Hist, vol. 107, No. 



2, p. 189. 



Shell medium to large sized (80 mm.), subelliptical, convex, smooth. 

 Periostracum gray-brown, shiny, varnish-like; beneath this, the shell is 

 gray-brown to purplish, usually with two brown rays running across the 

 umbones to the ventral margm and a series of zigzag m^^rkings heaviest 

 on the umbones. Interior of shell white or irregularly stained with purple 

 or violet. 



Length 79.5 mm., height 61.6 mm., diameter 39.2 mm. Pearl Islands, 

 Panama. 



This species is related to M. maculata (Linne) of the West Atlantic 

 but is more convex and its color pattern is somewhat different. 



Range — Lower California to northern Peru. Panama: Pearl Islands; 

 San Carlos; Bucaro; Burica Peninsula. Ecuador: Ancon Point; Galeras; 

 Manta; Isla la Plata; Santa Elena. Peru: Zorritos; Caleto Sal; Mancora. 



Subgenus MEGAPITARLV Grant and Gale. 19-31 



Macrocallista (Megapitaria) aurantiaca (Sowerby) Plate 46, figures 1-lc 



Cytherea aurantiaca Sowerby, 1831, Gen. Rec. and Foss. Shells, vol. 2, pt. 33, pi. 196, 



fig. 3. 

 Cytherea aurantia Hanley, Sowerby, 1851, Thes. Conch., vol. 2, Cytherea, p. 628, pi. 132, 



fig. 97 bis. 

 Dione aurantia Deshayes, Reeve, 1863, Conch. Icon., vol. 14, Dione, pi. 3, fig. 12. 

 Macrocallista aurantiaca (Sowerby) Maxwell Smith, 1944, Panamic Marine Shells, p. 



59, fig. 762. 



Full grown specimens are large (110 mm.), ovate, with solid por- 

 cellanous shell covered by a brown or mahogany colored periostracum under 

 which the surface is smooth, polished and usually of a pink or salmon color. 

 Internally, the ends of the hinge may be stained purple. Young shells have 

 the beaks white or cream, marked off by a zigzag line, the color below 

 usually brown but sometimes speckled with white or with zigzag markings. 



Length 98.4 mm., height 82 mm., diameter 54 mm. San Pedro, near 

 Manglaralto, Ecuador. 



Length 110 mm., height 87.5 mm., diameter of a left valve 28.7 mm. 

 Viveros, Pearl Islands, Panama. 



