CONCHOLOGY. 25 



er, obtuse, and perforated in the middle ; shell generally flex- 

 uous, of a brownish colour ; exterior rough, interior smooth. 



4. Septaria. One species. 



The tube of this genus unquestionably contains a bivalve 

 shell ; but, as no perfect specimen has yet been found, nothing 

 decisive is known respecting it. 



Tube calcareous, thick, conically elongated, more or less 

 flexuous, as if composed of pieces placed on the ends of 

 each other, or as if articulated, with a ring or projection 

 more or less marked at the place of the joints, but without 

 traces of partitions ; terminated on one side by an inflation, 

 oftentimes with some interior partitions, and on the other by 

 two tubes, distinct and sub-articulated. 



S. arenaria. The Sand Septaria. 

 The type of this genus. 



5. Teredina. Two fossil species. 



A genus without a living species, given here to preserve 

 the family entire, having a shell thick, oval, short, very gaping 

 posteriorly, equivalve, inequilateral ; summits well marked ; 

 a spoonlike cavity in each valve. 



Tube or sheath testaceous, cylindrical ; anterior end open ; 

 posterior end closed, but exhibiting the two valves of the 

 shell. 



6. Teredo. The Ship Worm. Three species. 

 This genus derived its name from the faculty it possesses 

 of boring wood. The T. navalis can penetrate the stoutest 

 oaken planks of a ship's sides by means of two valves af- 

 fixed to the head of the animal. The effects produced 

 would be much more destructive but from the fact of their 

 generally perforating the wood in the direction of the grain. 

 Sir E. Home wrote a very scientific and interesting descrip- 

 tion of a species not mentioned by Lamarck, called the T. 

 gigantea, found imbedded in indurated mud in the Island of 



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