230 



ZOOLOGY. 



corresponding cavity large and triangular. In Saxicava and 

 Panopcea (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 



Fig. 167.- 

 tural size. After 



errill. 



trilineata, na- 



Pltolas and Petricola. 

 said to be luminous. 



stone, as does GastrochcBna, 

 Many boring Lamellibranchs are 



Fig. 168.Cflycimeris siliqua, natural size. After Morse. 



A very aberrant form of bivalve mollusk is Cla-iciyella, 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 

 Asperyillum, 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- 

 pot. 



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 



