CONCHIFERA OR BIVALVES. 61 



to keep them together, separate and are 

 thrown in different directions. There are two 

 genera, Xylophaga and Pholas, both of which 

 bore into stones, wood, and madrepores. 



11. Xylophaga (Turton). Shell, valves 

 equal, inequilateral, and very much gaping, 

 very similar to those of Teredo. 

 They have no calcareous tube, S; 

 but two small accessory testa- 

 ceous pieces placed near the hinge, and one small 

 tooth in each valve, with an internal rib running 

 from the boss to the margin. 



These shells are found in light wood or 

 pieces of stick, which the animals penetrate to 

 the depth of about an inch.* 



12. Pholas. — Shell gaping at 

 both ends, equivalve and transverse, 

 having a flat, recurved, spoon- 

 shaped process in each valve below 

 the bosses, which are close to one 

 end of the shell, covered by a cal- 

 losity, and also having accessory 

 pieces attached. Animal having 

 two small united tubes at one end of the shell. 



Reeve's Con. Sys. 



