ADDENDA. 2ob 



It appears to have the same alliance to the Teredo, as the Gas- 

 trochagna has to the Pholaa. 



Careful maceration and dissection of some living specimens of 

 the Pholas lamellata, and Pholas crispata, having satisfied us that 

 there are small accessorial valves at the back of each. We suppose 

 therefore that it may be considered as an established conclusion, 

 that in those bivalve shells which are furnished with accessorial 

 valves or appendages, of a different shape and structure from the 

 primary ones,''there is no permanent ligament ; and that when there 

 is a permanent ligament, either externally or internally, there are 

 no accessorial valves. 



TEREDO. 



Teredo valvis postice auriformibus auriculis reflexis, accessoriis trans- jiaileolus 



versis malleiformibus. 

 Shell with the valves ear-shaped behind and the auricles reflected, 



the accessorial valves transverse and mallet-shaped. 

 Tab. nost. 2, fig. 19. 

 Mus. nost. From timber in Torbay, 



Shell a quarter of an inch in diameter ; and is distinguished 

 from the Teredo navalis, in having distinct auricles underneath, 



