ADDENDA. 255 



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

 Gastrochaena has to the Pholas. 



Careful maceration and dissection of some living specimens 

 of the Pholas lamellata, and Pholas crispata, have 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 struc- 

 ture 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, aveessoris Maiifoius 



transversis malleiformibiis. 

 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, 



