230 ZOOLOGY. 
corresponding cavity large and triangular. In Sazicava ana 
Panopea (Fig. 170), the pallial line is represented by a 
row of dots. In Macoma (Fig. 
171) the siphons are very long. 
Lithodomus, the date shell, 
one of the mussels, bores into 
corals, oyster shells, etc.; the 
. = common Saxicava excavates 
sonnei LHaiptong trilineata, na- holes in mud and soft lime- 
stone, as does Gastrochena, 
Pholas and Petricola. Many boring Lamellibranchs are 
said to be luminous. 
Fig. 168.—Glycimerts siliqua, natural size.—After Morse. 
A very aberrant form of bivalve mollusk is Clavagella, in. 
which the shell is oblong, with flat valves, the left cemented 
to the sides of a deep burrow. The tube is cylindrical, 
fringed above and ending below in a disk, with a minute 
central fissure, and bordered with branching tubules. In 
Aspergillum, the watering-pot shell, the small bivalve shell 
is cemented to the lower end of a long shelly tube, closed 
below by a perforated disk like the “rose” of a watering- 
ot. 
: The most aberrant Lamellibranch is the ship-worm, Teredo 
navalis Linn, (Fig. 174). This species is now cosmopolitan, 
and everywhere attacks the hulls of ships and the piles of 
wharves. It is one of the most destructive to human inter- 
ests of all animals. The body is from one to two feet long, 
slender, fleshy; it lives in a burrow lined with limestone, 
while the shell itself is globular, and lodged at the farther 
