TEREDO. 29 



are lined with their solid white tubes, at the l)ottom of which the 

 shell is found, Tlio shell itself is small, the two 



, , . T FiK.355. 



valves touching each other at only two points, and 

 so much arched that when in position they form 

 a mere ring. 



It is occasionally found in ship-timber, especially 

 wliere it has been exposed to a tropical sea, and 

 is familiarly known by the name of the ship-ivorm. 



The above terms would apply to any species of 

 Teredo, of which several are now recognized, llie 

 true T. navalis, as now understood by conchologists, seems to be 

 very seldom, perhaps never, met with in the Nortli Atlantic waters, 

 where it is replaced by what is now regarded as distinct, T. Nor- 

 vag'ica, the two having until recently been confounded. Its princi- 

 pal characters arc its rather thin valves of about equal height and 

 length ; anterior auricle medium size, connected with a narrow 

 marginal area, both of which are radiately finely grooved ; poste- 

 rior auricle expanded, its upper margin sloping from the beak, ter- 

 minating lower down than the anterior area, divided from the fang 

 by a channel, and internally shelving over the cavity of the shell ; 

 um1)onal blade flattened and twisted, not dilated at tip. Pallets 

 convex on one side and plane on the other, sliovel-shaped, emar- 

 ginate at tip, the stalk about as long as the blade. Tube solid, 

 flexuous, not chambered. 



Diameters about one fourth of an inch. 



A few specimens which answer well to this description have 

 been taken from ship-timber, but I am unaljle to certify as to its 

 habitat. Its history was originally made out in great detail in 

 Holland, where its ravages were most serious. 



Teredo Norvagica. 



Length short compared with height ; auricles about on a level, not ascending, 

 inner margin of wing shelf-like. Pallets shovel-shaped, with a small subter- 

 minal muscular impression. 



Teredo Norvarjica, Spenglek, Skrivt. Nat. ii. 102, pi. 2, figs. 4-6 (1792). —Forbes and 

 Hanl., Brit. Moll. i. 67, pi. 1, figs. 1 -5.— Jeffreys, Ann. and Mag. Nat. Hist. 3d 

 ser. vi. 121. — Tkyox, Proc. Acad. Nat. So. Philad. (Sept. 1862), 470, where also see 

 full synonymy. 



Teredo Norvegica, Adams, Genera, ii. 333, pi. 90. figs. 6a to d. — Chenu, Man. de 

 Conch, ii. fig. 60, 61. — Sowerby, Illustr. Brit. Sh. pi. 1, fig. 2. — Woodward, 

 Man. pi. 23, fig. 26, 27. 



Teredo navalis, of all the earlier English and French naturalists. 



