PANAMIC-PACIFIC PELECYPODA 445 



Shell elongate, white, relatively thin, the anterior margin rounded or 

 beaked, the anterior ventral or pedal gap varying in size from a narrow 

 slit to broadly ovate. Accessory plates two, consisting of a protoplax and 

 mesoplax, the protoplax chitinous or only slightly calcified. Umbonal re- 

 flection well separated from the surface of the umbones, the space between 

 empty, not septate. 



Divided into two subgenera as follows: 



I. Valves beaked anteriorly. Pedal gap ovate and large. 



Subgenus Cyrtopleura, s.s. 



II. Valves rounded anteriorly, the pedal gap small, slitlike. 



Subgenus Scobinopholas 



Subgenus CTRTOPLEUKA Tryon, s.s. 



Cyrtopleura (Cyrtopleura) crueller (Sowerby) Plate 78, figure 3-3b 



Pholas cruciger Sowerby, 1834, Proc. Zool. Soc. London, p. 69. "In soft sandstone, 

 Island of Puna in the Gulf of Guayaquil; in soft stone at low water in the 

 Bay of Caraccas; and in hard clay in the Gulf of Nocoiyo [Nicoya]." 



Pholas crucifera Sowerby, 1849, Thes. Conch., vol. 2, p. 489. 



Pholas crucigera Sowerby, 1849, idem., pi. 104, figs. 24-26. 



Cyrtopleura (Cyrotpleura) cruciger (Sowerby), Turner, 1954, Johnsonia, vol. 3, No. 33*, 

 pp. 41-43, pis. 17, 20, 21. 



This pholad is a borer in soft rock. The shell is generally small, seldom 

 exceeding two inches in length, white, its surface usually with a chalky 

 appearance. Valves are elongate, uniformly convex throughout, highest just 

 behind the beaks, the dorsal and ventral margins are straight and nearly 

 parallel, the anterior-ventral margin with an expanded, ovate-lanceolate gap. 

 The sculpture is formed by fairly strong, radial riblets, coarser towards the 

 anterior end, fading out and becoming replaced entirely on the extreme 

 posterior end by concentrics. The concentrics as they pass over the radial 

 riblets form vaulted, imbricated scales, the posterior arm of the V more or 

 less in line. 



Range — Mexico south to northern Peru, Colombia: Isla del Gallo. 

 Ecuador: Galeras; Sua; Manta; Puna. Peru: Tumbez. 

 Subfamily MARTESIINAE 



Borers in soft rock, shell or wood. Characters of the shell as given in 

 the key. 



I. Valve with a single sulcus extending from the beak across the umbone 

 to the ventral margin dividing the surface of the disk into two sections. 



A. Callum with an extension between the beaks and along the ventral 

 margins, the metaplax small and placed entirely behind the beaks. 

 Rock borers. 



Genus Hastasia 



B. Callum without dorsal and ventral extensions. Metaplax large, covering 

 the beaks and umbones. Wood borers. 



Genus Martesia 



II. Surface of valves with two sulci extending across the disk and dividing 

 it into three sections. 



Genus Parapholas 

 Genus MARTESIA Sowerby, 1824 



(Hiata Zetek and McLean, 1936) 

 Type species by monotypy, Pholas clavata Lamarck (= P. striata 

 Linne). Western Europe, cosmopolitan. 



