Pholadidae and Teredidae 95 



oblique sulcus. Anterior area ribbed by toothed ridges; posterior 

 area shows only growth lines. The posterior shield (protoplax) is 

 lanceolate with a median, longitudinal furrow and oblique radiating 

 sulci. 



The mollusks usually bore into wood, sometimes into soft rock. 



Martesia striata' ^7 (Linne) PI. 19, figs. 127a, b 



Alt., 10; length, 35 mm., in favorable circumstances 50 mm. 

 Shell narrowly cuneate, prolonged posteriorly; anterior aspect cordi- 

 form, with sinuous, crenulate ridges and delicate radial sculpture; 

 posterior area shows only wavy growth lines. A narrow, shallow 

 sulcus separates the two areas. The protoplax is normally trilobed; in 

 young and stunted specimens the lateral lobes may be suppressed and 

 the shield somewhat trigonal. 



This Martesia penetrates hard wood. 



The juvenile of this species is so different in appearance that 

 It has been described as a new species by several authors, but a 

 study of the life cycle proves it to be the same shell. The anterior 

 margins are widely gaping and the shell being much shorter than 

 the adult, assumes a slightly heart-shaped appearance. An illustra- 

 tion of the juvenile appears on Plate 45, figure 127c. 



Family TEKEDIDAE 



Teredo is a name given by Pliny to a wood-eating worm. Even 

 before Pliny's time, the shipworm was recognized as an agent of 

 destruction to wooden ships, and today, the ravages of this mollusk 

 in wooden structures is a costly matter; no wood is known to be 

 wholly resistant to attack. Shipworms have been cultivated in soft 

 wood, and collected for food when the desirable size attained. Their 

 distribution is world-wide. 



The mollusks of this family have evolved an aberrant form; 

 they are elongate, wormlike, with only the anterior extremity 

 covered by the small, bivalve shell. 



The life history of no one species is fully known; some dis- 

 charge the ova into the sea, some are viviparous. The larvae all have 

 bivalve shells, and swim freely for a short time but soon attach 



167 Lat, striatus, channejed. 



