Dr. J. E. Gray on the Structure and Position of Teredina. 87 



to that genus by the Lamarckian conchologist, as soon as the 

 dorsal valves were discovered, and the genus Teredina erased 

 from the list, as it has all the characters of Pholas as defined by 

 Lamarck. 



This is an instance of the careless manner in which a single 

 species is elevated by some authors of that school into the rank 

 of a genus, because its structure has been misunderstood or be- 

 cause it possesses some slight peculiarity of external appearance, 

 while at the same time they retain, in other genera, a number of 

 species possessing forms which offer quite as important characters 

 to distinguish them. 



It only resembles Teredo in the shape of its valves, but is 

 immediately distinguished from it by the absence of the shelly 

 case of the cavity in the marine body in which it resides, in 

 the absence of any palettes (or opercula, as they are sometimes 

 called) at the sides of the ends of the siphons, and in the pre- 

 sence of the dorsal plate over the umbo, which is never present 

 in this genus. It has no affinity to such genera as Aspergillum, 

 Clavagella, or Gastrochcena, to which Lamarck, G. B. Sowerby*, 

 and many authors compared it, as it does not live in a tube, 

 the part which they described as a tube being only the sheath 

 of the siphons lapidified by the process of fossilization, as is 

 proved not only by its position as regards the valves, but also 

 by its bulging form, which shows that it was formerly soft and 

 yielding. 



Mr. G. B. Sowerby, in his 'Genera of Mollusca/ says this 

 genus "has an operculum, as we are informed, though we have 

 never seen it, which covers the double opening ;" and, further, 

 he says it differs from Pholas papyracea in "having an operculum 

 to cover the posterior aperture of the tube." I have searched 

 for these opercula or palettes in a large series of specimens with- 

 out discovering the slightest trace of them ; indeed, the siphons 

 are not formed as if they were present ; and the absence of the 

 tube covering the entire animal, siphon, and valves, with which 

 they are always combined, renders their presence not to be 

 expected. 



Mr. G. B. Sowerby describes them as " gregarious, occurring 

 in numbers in a bed of ferruginous sand," " living in cavities of 

 its own terebrating." He further observes, " That in its young 

 state it is destitute of a tube, and consists only of two valves 

 and a membranaceous envelope, we cannot doubt." I do not 

 believe that there is any difference between the old and young 

 in this respect, as in both states I think it is evident the tube 



* Mr. G. B. Sowerby observes that " the tube in Teredina never covers 

 the two valves, but appears to be soldered to them, as in Aspergillum." (!) 

 (' Genera.') 



