TEREDO. 79 



and dorsally, and (in the adult, at least) occupies more 

 than one-half of the posterior side. The front triangular 

 area is small, and acutely pointed ; its base, which is pe- 

 culiarly straight and oblique, lying much above the level 

 of that of the auricle. The front dorsal line is very short, 

 and scarcely, if at all, declining ; the lower anterior edge 

 is rectilinear, and rarely inclining inwards to meet the more 

 or less convex and rapidly sloping margin of the posterior 

 side, with which it forms a somewhat rounded point. 



The subumbonal blade is so placed as to present its 

 broader surface to the inner disc ; it is narrow, not par- 

 ticularly elongated, tapering, and not at all jagged at the 

 edge. The callosity of the hinge-margin is well developed, 

 projects above the dorsal level, and slants with a strong 

 posteriorward inclination : the ventral callosity is solid and 

 prominent, but not widely expanded. 



The pallets, which, like those of Norvagica, resemble 

 the shape of a battledore, approach so nearly to those of 

 that species, as with difficulty to be distinguished, except 

 by direct comparison. We may then perceive that the 

 handle or stalk is much less elongated in proj)ortion, and 

 tapers to a fine point at its apex, (in the other it is blunt at 

 its termination, and solid throughout.) In the only five 

 specimens of this portion which we have hitherto seen, and 

 which, not being above a quarter of an inch long, we can- 

 not pronounce adult, the position of the stalk upon the 

 interior surface of the broader terminal plate is most dis- 

 tinctly manifested throughout, and externally there is a 

 distinct groove on either side of it at its insertion in the 

 plate. The latter, which is somewhat abbreviated in form, 

 has its sides curling inwards, somewhat in the fashion of 

 those of malleolus, (the stalk is, however, not bent as in 

 that rare species ; ) and, although the base is almost straight, 



