T. navalis. 



TEREDO. 29 



are lined with their solid white tubes, at the bottom of which the 

 shell is found. The shell itself is small, the two 

 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 

 where it has been exposed to a tropical sea, and 

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



The above terms would ap[)ly to any species of 

 Teredo, of wl'ich several are now recognized. The 

 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 ha\'ing until recently been confounded. Its princi- 

 pal characters are its rather thin valves of about equal lieight 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 ; 

 umbonal blade flattened and twisted, not dilated at tip. Pallets 

 convex on one side and plane on the other, shovel-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 shii>timber, but I am unable 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 Its history was originally made out in great detail in 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 Norvacfica, Spengler, Skrivt. Nat. ii. 102, pi. 2, figs. 4-6 (1792). — Forbes and 

 IIan-l., Brit. Moll. i. 67, pi. 1, fisj.s. 1 -.5. — Jeffreys, Ann. and Mag. Nat. Hist. 3d 

 ser. vi. 121. — Tryox, rroc. Acad. Nat. Sc. Pliilad. (Sept. 1862), 470, where also see 

 full sj-nonymy. 



Teredo Norvegica, Ad.\ms, Genera, ii. 33.3, pi. 90. figs. 6a to d. — Chenu, Man. de 

 Conch.il. fig. 60, 61. — Sowerbv, Illustr. Brit. Sh. pi. 1, fig. 2. — Woodward, 

 Man. pi. 23, fii;. 26, 27. 



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



