TEREDO. : 41] 
° 
miform of all the mollusca, forms tortuoug. cylindrical 
hollows in wood; and in some climates commits the most 
extensive injuries to ships, the piles of harbours, bridges, 
and other submarine works formed of timber. A reference 
to the illustration given by Sir C. Lyell will render detailed 
description unnecessary. The Zeredo is furnished at one 
extremity with testaceous valves, by which it bores its way 
into the wood, while from the surface of its soft body a 
calcareous matter is secreted, which lines with a shelly 
covering the hollows or channels formed by the animal in 
its progress. The fossil species differ from the recent in the 
valves being united to the calcareous tube. Wood perforated 
by Teredines, and occupied by their shelly tubes, occurs in 
almost every locality of the London Clay. Those specimens 
in which the wood is petrified, and the cavities of the tubes 
are filled with calcareous spar of various colours, furnish 
beautiful sections, when cut and polished (Pict. Atlas, pl. 
viii. fig. 8,9). When the canal in the Regent’s Park was 
being formed, large blocks of perforated calcareous wood 
were discovered, having the ligneous structure well preserved, 
and the tubes of the Teredines occupied by yellow, grey, 
and brown spar, forming specimens of great beauty and 
interest. Wood, with Teredines, or some analogous boring 
mollusks, occurs sparingly in the chalk of this country ; 
but in the cretaceous strata at Maestricht, large masses are 
frequently found.* Fossil wood may occasionally be ob- 
served with perforations that have been made by other 
kinds of boring shells; but the preceding remarks will 
suffice to convey an idea of the nature and origin of such 
appearances. T 
* In the British Museum there is a mass of silicified wood from 
the Upper Green-sand of Blackdown, perforated by a Teredo, whose 
valves remain in the burrows. 
+ Other genera of boring shells also occur fossil, as Fistulana, 
Gastrochena (Min. Conch. tab. 526), Saxicava (Min. Conch. tab. 466). 
