TEREDO. 75 



cies, inadequately defined by the language of its author, 

 and only specifically limited by his references to the en- 

 gravings of that author and of Vallisnieri, the latter irre- 

 cognisable, depends, but also by personal examination of 

 the examples still preserved in the cabinet of the illustrious 

 Swede. 



The casque-shaped valves (as well as the tube and pallets) 

 are of an uniform white ; the sculpture of the former exhibits 

 no peculiar features, the front triangular area being finely 

 and rather closely lyrated concentrically; the succeeding, 

 oblique, and crowded striae, which run parallel to the lower 

 anterior edge, and subrectangularly to the lyrse, being mi- 

 nutely decussated, or even subgranulated, and the remain- 

 der of the surface comparatively smooth, although, in some 

 of the younger examples, the striae of growth are so deve- 

 loped, as almost to give a finely plicated appearance to that 

 portion of the shell. 



The front triangular area is in general rather large, ab- 

 ruptly severed, as it were, from the body by a more or less 

 impressed line, and having its base more convex than in the 

 succeeding or preceding species, not particularly oblique, and 

 always much above the level of that of the auricle. The 

 lower anterior edge slopes a little backwards, and forms a 

 rounded point with the short and somewhat arcuated lower 

 margin of the hinder side. The auricle, whose commence- 

 ment is easily perceived by the abrupt sinking of the level, 

 is of a moderate size, somewhat pear-shaped internally, late- 

 rally and never dorsally projecting, and in typical examples 

 seated low down, so that the general inclination of the pos- 

 terior hinge margin is more sloping than in most of the 

 known Teredines. Its lower edge is more or less arched ; its 

 upper, whether it runs retusely, straightly, or more rarely 

 convexly to the beaks, forms an uninterrupted line with the 



