TEREDINA. 



while the anterior part and the two valves are like a soft 

 shelly substance. In form the two valves exactly resem- 

 ble those of Teredo; in Teredina, however, these are 

 wholly external, and they are thickly lined as well as 

 united to the tube by a continuation of the shelly matter 

 of which the tube itself consists. The beaks or umbones 

 of these two valves are very much incurved, and covered 

 by a rather quadrangular thick accessory piece which 

 appears to be fixed to the valves in front of the beaks; 

 and there is an irregular prominence of the tube just 

 behind the beaks. The anterior termination of the tube 

 is completely closed by a trapezoidal piece which fills up 

 the space left by the sinus in the two valves. The testa- 

 ceous matter is generally so much increased in thickness 

 internally, as nearly to obliterate or cover the internal 

 appendages usually called the teeth, common to it and 

 Teredo. 



The Teredina appears to have been gregareous, as it 

 occurs in numbers in a bed of ferruginous sand at the 

 only place in which it has been found; there is no reason 

 to doubt its habit of living in cavities of its own tere- 

 brating, but whether in wood or any other substance, we 

 have not the means of ascertaining. That in its young 

 state it is destitute of a tube, and consists only of the 

 two valves and a membranaceous envelope we cannot 

 doubt, and it appears to us probable that in this respect 

 as well as in the habit of terebrating sandstone it is 

 nearly analogous to the Pholas papyracea.* 



Fig. 1. Teredina personata, showing the ventral portion together with the 

 double aperture. 



2. The form of the aperture 



3. The dorsal portion showing the beaks. 



4. The same having the beaks covered with the accessory valve. 



* For notwithstanding the opposition which our opinion formerly expressed 

 has mot with, we must still maistain that the PA. /fl>«e//a^a of Turton is only 

 the young of i*h. papyracea. 



