230 



ZOOLOGY. 



correspQn^ag cavity large and triangular. In Saxicava and 

 Pampaa (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 

 in mud and soft lime- 

 stone, as does Gastrochmna, 

 Many boring Lamellibranchs are 



tural 



ig. 167.- 

 Isize.— . 



■After 



vhora trilineaia, na- Tioles 



PJiolas and Petricola. 

 said to be luminous. 



;, natural size.— After Morse. 



A very aberrant form of bivalve moUusk 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- 

 pot. 



The most aberrant Lamellibranch is the ship-worm. Teredo 

 navalis Linn. (Fig. 174). This species is now cosmopolitan, 

 and everywhere attacks th© 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 i» a burrow lined with limestone,, 

 while the shell itself is globular, and lodged at the farther 



