MARINE MOLLUSCA OF THE UNITED STATES. 129 



prominent, nearly terminal ; hiatus narrowly elongate, nearly ex- 

 tending the total length of the shell ; dorsal and ventral margins 

 nearly parallel. 



Length 16, alt. 6 mill. 



Beaufort, N. C. (W. Stimpson.) 



Family TEREDIDJE, Carpenter. 

 Lectures on Mollusca, 100. 1861. 



The shelly tube of the ship-worm is subcylindrical, divided 

 longitudinally and often concamerated by numerous, incomplete, 

 transverse partitions ; the siphonal palettes or stylets assist in 

 compressing and relaxing the siphons to facilitate the flow of 

 water through the long canal. 



The Teredines live in most seas, perforating wood in the direc- 

 tion of the grain by means of the mechanical attrition of their 

 valves ; these tortuous perforations are lined by calcareous matter 

 forming the tubes. The animal is useful in destroying fragments 

 of wrecks and floating timber, but causes great destruction to 

 dikes, wharves, and to ships when the timbers are not protected 

 from its ravages.. 



Synopsis of Genera. 

 Pallets simple. • Teredo. 



Pallets compound, the blade penniform, composed of a number of jointed 

 setae. Xylotrya. 



Genus TEREDO, Linnajus. 

 Syst, Nat., edit, x., p. 651. 1758. 



1. T. dilatata, Stimpson. Figs. 272, 273, and 274. 

 Bost. Proa, iv. 113. 1851. 

 Diameters nearly equal ; wing lai'ge, not ascending so high as 

 the beak, but passing off from it by a gentle slope, descending 

 below the anterior triangle, having no defining exterior groove, 

 slightly concave and then reflected outwards on the internal face; 

 pallets very small, battledore-shaped ; end of tube concamerated. 

 Length and alt. 12.5 mill. 



Massachusetts to So. Carolina. 

 This species differs from T. megotara, Hanley, which it greatly 

 resembles, in the smaller altitude of the valves, the greater breadth 

 of the auricle, which is also placed much lower, and in its con- 

 camerated tubes. 

 9 



