72 PHOLADIDiE. 



cimens have from one and a half to two inches and upwards 

 of the smaller end of the tube greatly contracted within 

 by lamina3, also the partition producing the double aperture 

 extending but a few lines from the very extremity. The 

 greatest thickness of the shell is at the smaller end, where, 

 at the commencement of the laminse, its consistence is from 

 one -twentieth to one-fortieth part of an inch: from this 

 it b£Comes gradually thinner towards the greater end, which 

 in the very largest specimens is found to be closed up ; but 

 in several others there is no deposition whatever of testa 

 ceous matter for some distance from the termination of the 

 cell. In one perforation, about twenty inches long, the 

 body of the animal has had no testaceous covering for the 

 last three and a half inches ; in two other cells, of about 

 two feet, no deposition appears for four and a half and 

 four inches and three-quarter from their termination. All 

 the timber at Portpatrick in which the Teredo had formed 

 its habitation is pine; and perhaps to this circumstance the 

 superior size of the animal may chiefly be attributed. 

 ThouQ'h it is well known that the Teredo bores in the di- 

 rection of the grain, it may be observed that it does so whe- 

 ther the position of the wood be perpendicular or otherwise. 

 Captain Fayrer remarked that it has a decided disposition 

 to work horizontally. It is, however, often obliged to de- 

 viate from a straightforward course, to avoid such obstruc- 

 tions as nails, timber-knots, and the tubes of its fellows, and 

 make a winding or angular habitation, according as such 

 impediments occur; but these circumstances seem not even- 

 tually to impede the progress of the animal, as some of the 

 very largest specimens I have examined are the most tor- 

 tuous. During the nine or ten years that the Teredo has 

 been established at Portpatrick, it has not degenerated, as 

 specimens just received, which were alive in their native 



