316 AXEL A. OLSSON 



Shell elongated, pholadiform, regular in shape, never distorted, usually 

 thin. Surface is sculptured much like that of Pholas, the anterior set of 

 ribs large and sharply squamose, the others across the middle and posterior 

 slope simple, often reduced to small cords. Hinge with three, cardinal teeth 

 in the left valve, the middle one large, bifid, the others small; the right 

 valve has two cardinal teeth, both bifid, the posterior one more strongly 

 so. The pallial sinus is large, rounded at the end. 



The surface of the valves sculptured in a regular fashion with noded 

 or scabrous ribs, as well as by their shape and thin texture, have shells 

 which superficially resemble those of a pholad but can be distinguished at 

 once by their hinge bearing interlocking teeth. Found boring in the softer 

 types of rock such as shale and clay. 



Petricola (Petricolaria) parallela Pilsbry and Lowe Plate 54, figures 3-3b 



Petricola gracilis parallela Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Philadelphia, 

 vol. 84, p. 99, pi. 13, fig. 4.— Maxwell Smith, 1944, Panamic Marine Shells, p. 

 62, fig. 797. 



Petricola {Petricolaria) parallela Pilsbry and Lowe, Hertlein and Strong, 1948, 

 Zoologica, vol. 33, pt. 4, No. 13, p. 195. 



The long or moderately slender shell is thin, white, or cream-colored 

 with the posterior end brown, sculptured like Pholas, the ribs on the an- 

 terior side strong, coarsely noded or scabrous while posteriorly the ribs 

 grade into fine threads. Lunular region excavated and smooth. 



Length 41.2 mm., height 13.3 mm., diameter 33.2 mm. Bucaro, Panama. 



This species resembles the East American P. pholadiformis but is 

 somewhat heavier and more slender. The largest specimen seen has a 

 length of about 44.3 mm. 



Range — Gulf of California southward to Panama. Nicaragua: Corinto 

 (Pilsbry and Lowe). Panama: Bucaro. 



Petricola (Petricolaria) cognata C. B. Adams Plate 54, figures 5, 5a 



Petricola cognata C. B. Adams, 1852, Ann. Lyceum Nat. Hist. New York, vol. 5, pp. 

 510, 546, 547, No. 477.— Pilsbry and Lowe, 1932, Proc. Acad. Nat. Sci. Phila- 

 delphia, vol. 84, p. 99, pi. 13, figs. 10, 11 (figs, of type).— Turner, 1956, 

 Occas. Papers on Mollusks, Mus. Comp. Zool., vol. 2, No. 20, p. 38, pi. 19, 

 figs. 3, 4. 



Shell pholadiform, dingy white. Sculpture on the posterior half of 

 shell consists of fine radial threads which become much coarser anteriorly 

 where they assume the character of riblets. Similar in general characters 

 to the East American P. pholadiformis but differs by the much more massive 

 teeth particularly in the right valve, the broader nymphs, and the wider 

 lunule-like area free of radial sculpture. It is a thick shell for Petricolaria 

 with strongly impressed adductor scars and pallial sinus. 



This species known as yet only from the type, first figured by Pilsbry 

 and Lowe, and recopied here. The above description is a partial revision 

 from that of Adams and from Pilsbry and Lowe. 



Range — Panama. Panama: Panama. 



