PHOLAS. TEREDO. 87 



shell, have the hinge furnished with an external ligament, and 

 ormed on each side with two or three projecting and very de- 

 cided teeth. Their foot is conical and is pushed out at the anterior 

 extremity of the shell. They live in the sand, and bury them- 

 selves with great rapidity hy the motions of their foot. 



17. The PHOLADES are distinguishable from all the preceding 

 by one or more calcareous pieces, situate between the two valves 

 of the shell, near the hinge. The valves, which are broad and 

 convex anteriorly, are elongated on the opposite side, and leave 

 betwixt them, a great oblique opening at each end ; their hinge 

 resembles that of the Mycs ; their double tube is not retractile 

 and may be very much elongated. These animals inhabit tubes 

 or long cells, which they excavate, either in the mud, or stones 

 or wood. There are large species on the coast of France, in the 

 West Indies, and on the coast of Peru. 



18. The TEREDINES, or ship worms, are celebrated for the 

 ravages they commit by boring into ships' bottoms, piles of 



.dikes, bridges, &c. These are mollusks with a 

 very elongated and almost vermiform body, which 

 is enveloped in a tubular mantle, open at the 

 anterior and inferior part for the passage of the 

 foot ; it is provided posteriorly with two very short, 

 distinct tubes, and its base is furnished on each side 

 with a movable stony plate ; the shell is composed 

 of two rhomboidal valves, but is very small, and 

 covers only a very small portion of the mantle. It 

 seems that the animal, by moving the extremity 

 of its shell like an auger, excavates, in submerged 

 wood, the hole which serves as its abode, and, as it 

 advances or buries itself deeper, it lines the exca- 

 vation with a calcareous mutter, so that in a short 

 time it finds itself lodged in a stony tube, which at 

 first might be mistaken for a second shell. It 

 begins its attack upon wood when very young; 

 hence the external opening of its gallery is very 

 small, but it digs on until the termination of its 

 growth, and progressively augments the size of its . 

 dwelling; the two tubes which occupy the posterior TJ*IIOL 

 extremity of the mantle always remain near the 

 opening of the gallery, and through one of them it causes the 

 water necessary for respiration and nutrition to enter, for it 



1 7 How is the genus Pholas characterized ? (Pholas, from the Greek, 

 pholfoi, a lurking-place.) 



18. What are the characters of the genus Teredj? (Teredo, Latin, a 

 hip-worm.) 



