446 AXEL A. OLSSON 



Borers in wood. Shell pholadiform, wedge-shaped, thin, white, inequi- 

 lateral, the surface of the valves divided into two sections by an umbonal- 

 ventral sulcus, the anterior portion sculptured with fine, toothed, concentric 

 ridges which are deeply inflexed near the middle, the posterior portion 

 with larger, smoother concentrics which are wholly absent from the more 

 extreme end. Anterior side of shell is widely open in the juvenile stage 

 (Hiata stage), later closed off by a large, paired callum. There is no proto- 

 plax, its place taken by the much enlarged, shieldlike metaplax, at first 

 relatively soft and wrinkled, later becoming more indurated. Metaplax 

 and hypoplax are both present, long and narrow in shape. The internal 

 apophyses are slender and hook-shaped. 



Following Turner, the genus is divided into two subgenera as follows: 



I. Mesoplax ovate to subcircular. Metaplax and hypoplax pointed or 

 truncated behind, not divided. 



Subgenus Martesia, s.s. 



II. Mesoplax wedge-shaped or cuneiform, metaplax and hypoplax divided 

 posteriorly. 



Subgenus Praticoma 



Martesia (Martesia) striata (Linnd) Plate 79, figures 6, 7, 7a 



Pliolas striata Linne, 1758, Systema Naturae, ed. 10, p. 669 western Europe. 



Hiata infelix Zcttk and McLean, 1936, Nautilus, vol. 49, No. 4, pp. 110, 111, pi. 8, 



tjgs. 1-4. 

 Martesia tntercaiata 'Carpenter' Hertlein and Strong, 1950, Zoologica, vol. 35, pt. 4, 



No. 19, p. 250. (i'^ot M. intercalata Czi^enui=^FenitetLa conradi [Vai.J). 

 Martesia {Martesia) striata (Linne), Turner, 1955, Johnsonia, vol. 3, No. 34, pp. 103- 



111, pi. 35, figs. 61-64. 



For full synonym and discussion of this species, the reader is referred 

 to Turner. 



Shell white, thin, variable in shape and often deformed, generally under 

 two inches in length. Undeformed specimens are elongate, the posterior end 

 of the shell produced and flattened, closed. Anterior section of the valves 

 in front of the umbonal-ventral sulcus is neatly scultpured with close-set, 

 denticulated concentrics, smooth and large just behind the sulcus and 

 absent entirely on the extreme posterior end. Young specimens {Hiata) 

 have no callum, the anterior side is widely open but this becomes closed 

 or roofed over by a large, paired callum in the adult. The mesoplax is large, 

 cuneiform, constricted in the middle, narrower in front, and with four 

 large, rounded corners. 



A common borer in wood. Specimens collected in Panama from stranded 

 piling at Venado Beach showed both the young Hiata stage without callum 

 and the adult form with the callum. 



Martesia jragilis Verrill and Bush, a nelaeic species, tak'^n mostly from 

 floating wood, is recorded from the Gulf of Panama by Tucker; closely 

 related to M. striata, it is distin<^uished by its depressed keeled-edged meta- 

 plax sculptured with concentric lines. 



Range — Atlantic from North Carolina to Brazil, the Gulf of Mexico 

 and the Caribbean. Pacific Coast of Mexico south to northern Peru. Also 

 Japan, the Hawaiian Islands. Panama: Guanico. Panama Canal Zone: 

 Venado Beach. Colombia: Isla del Gallo; Tumaco. Ecuador: Sua. Peru: 

 Tumbez. 



