462 MARINE INVERTEBRATES 
curious; it may be observed also in several deep-sea genera and in cer- 
tain extinct fossil forms. The length of this shell is about two inches, 
This species also occurs in California, 
where its favorite station is in hard tena- 
cious clay. Length two to four inches. 
FAMILY TEREDINIDE 
Genus Teredo 
T. navalis. This species is worm- 
like in form, but 
it has a small bi- 
valve shell at the 
larger end, and 
near the anterior 
extremity two 
caleareous ap- 
pendages called 
pallets, beyond 
which extend two 
siphons. Along 
the surface of the 
scene is secret- 5 
ed a continuous Zirphea crispata. 
shelly tube which eat: 
lines the burrow. This mollusk, commonly called 
the “ ship-worm,” is exceedingly destructive, per- 
forating with its burrows submerged timber 
and soon rendering it useless. Various means 
are taken to protect ships, the piles of wharves, 
buoys, and the like, against its ravages; copper 
sheathing, large-headed nails driven close to- 
gether into the wood, verdigris paint, and so 
on, being used with more or less effect. Vast 
numbers of these animals enter the wood and 
burrow in various directions, but they never 
interfere with one another, a thin partition of 
wood always being left between adjacent bur- 
rows. How they effect the burrowing is not 
determined, but it is supposed to be by means 
of the pallets. Teredo does not, like the boring 
isopod Limnoria lignorum, feed upon the wood. 
Its food consists of microscopic organisms which 
are taken in through the incurrent siphon. In 
temperate waters T. navalis grows sometimes to 
the length of six inches; in tropical waters it 
attains the length of two feet. 
There are three other species of Teredo and one 
af the genus Ales on our Northern shores ij 
oy Mala in L: navalis is, however, the most common an 
oe pee oes peti most destructive. In Southern waters there are 
T, tube; V, valve of shell. many other forms of these boring mollusks. 
