230 



ZOOLOO T. 



corresponding cavity large and triangular. In Saxioava ano 

 Panopcea (Fig. 170), the paUial Une 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 exeayates 

 mud and soft lime- 

 stone, as does Gastrochmna, 

 Many boring Lamellibranchs are 



Fie. \SI.—Clidl 

 tatalsize. — ^After 



?ertS."^'"^^' "*■ lioles in 

 as 



Pholas and Petricola. 

 said to be luminous. 



Pig. 168.- GlydmerU sUiqua, nataral size.— Alter Morse. 



A very aberrant form of bivalve mollusk is Cla'togella, 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 LameUibranch 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 



