PANAMIC-PACIFIC PELECYPODA 145 



covers half of the inside surface of the valve. 



Atrina (Serratrlna) maara (Sowerby) Plate 18, figures 6, 7; 



Plate 55, figure 1 



Pinna maura Sowerby, 1835, Proc. Zool. Soc. London, p. 84. Panama. — Reeve, 1858, 



Conch. Icon., vol. 11, Pinna, pi. 29, fig. 54. 

 Pinna [Atrina] maura Sowerby, Maxwell Smith, 1944, Panamic Marine Shells, p. 50, 



fig. 672. 

 Atrina maura (Sowerby), Hertlein and Strong, 1943, Zoologica, vol. 28, pt. 2, p. 165. 

 Pinna lanceolata Sowerby, 1835, Proc. Zool. Soc. London, p. 84. — Reeve, 1858, Conch. 



Icon., vol. 11, Pinna, pi. 31, fig. 39. Name preoccupied. 



The shell is elongate, fan-shaped, sometimes quite large (about 230 

 mm.), thin, brown, subtranslucent, the posterior end wide, its margin 

 straight, truncated, the ventral margin nearly straight, except for being 

 slightly impressed anteriorly. The sculpture is formed by 8 to 12, nearly 

 straight rows of high, fluted to tubular spines on the middle and dorsal 

 surface, subobsolete along the ventral side. 



This species resembles A. rigida Dillwyn of the Atlantic but has a 

 narrower form and the anterior-ventral side is less deeply impressed. 



Range — Lower California to northern Peru. Panama: Taboga Island. 

 Canal Zone: Venado Beach. Ecuador: Esmeraldas; Cojimenes; Puerto Callo. 

 Peru: Tumbez. 



Family PTERIIDAE 



To this family belong the Pearl Oysters represented in the fauna by 

 two genera, Pteria (Avicula) and Pinctada (Margaritiphora) distinguished 

 by their pearly interiors and aviculoid or wing-shape. The valves are 

 aviculoid to suborbicular in form with a small anterior wing below which 

 in the right valve is a deep notch for the passage of a byssus. Inner layer 

 of shell is brilliantly pearly or nacreous, thin or heavy, the outer layer 

 prismatic and lamellar, often developing a wide, darker colored border to 

 the ventral margins. The dorsal margin or hinge line is straight, edentulous 

 in Pinctada; provided with long, lamellae-like teeth in Pteria. The ligament 

 is subinternal, the resilium portion attached to a shallow, scarlike depres- 

 sion or to a narrow groove, behind the beaks. External surface usually rayed, 

 often spinous. 



Key to genera of Pteriidae 



A. Shell relatively thin, convex, with a long, pointed or widely expanded 

 posterior wing. Hinge provided with one or two, small tubercular teeth 

 below the beak, and one or two long, horizontal, posterior lamellae 

 obliterated in large shells by the growth of the cardinal area. 



Genus Pteria 



B. Shell heavy, often large, suborbicular without a definite posterior wing. 

 Hinge edentulous at all stages. 



Genus Pinctada 

 Genus PTERIA Scopoli, 1777 

 Type species by monotypy, Mytilus hirundo Linne. Recent, Mediter- 

 ranean Sea. 



Shell obliquely aviculoid, the length along the hinge line longer than 

 the height, the ends auriculate, the posterior ear much larger, often pointed, 

 the anterior ear small, that of the right with a notch for the passage of 

 the byssus by which the shell is attached. Cardinal area generally narrow 



