135 



LAMELLIBRANCHIATA. 

 Teredo Suciensis. (N. Sp.) 



Plate 17, figures. 1, la. 



Shell globosely cordate ; valves very inequilateral, slightly longer than 

 high; test thin. Anterior side short; anterior auricle convex above, 

 pointed in front, truncated almost horizontally below, variable in size, 

 but usually very small. In six out of seven specimens the anterior 

 auricle extends from the beaks to one-third the distance from the 

 extremity of the ventral boi'der, but in the seventh it reaches as far 

 downwards as the middle of the front margin of the valves. Antei'ior 

 hiatus, as viewed in front, inversely triangular, higher than wide in the 

 majority of specimens, but in one instance only, wider than high. 

 Margin of the valves, as viewed laterally, truncated almost perpen- 

 dicularly, but a little obliquely, beneath the anterior auricle. Base 

 obtusel}^ pointed, posterior side longer than the anterior, nearly straight 

 above, narrowing obliquely and concavely from the base upwards, gaping 

 rather widely in its lower half and forming a bluntly pointed or narrowly 

 rounded junction with the cardinal margin above. Umbones prominent, 

 placed in advance of the middle ; beaks incurved and directed a little 

 forwards. 



The valves are divided into three subordinate areas, each of which has 

 its own peculiar shape and style of sculpture. The first of these is the 

 anterior auricle, whose surface is covered with densely crowded and 

 exceedingly minute, concentric strise which can only be seen by the aid 

 of a lens. The second is the central area, which is very narrow and 

 invariably marked by minute radiating stria barely visible to the naked 

 eye. Its upper poi'tion lies between the posterior area and the anterior 

 auricle, from which latter it is sometimes separated by an impressed line 

 or slight shoukler, and below the auricle it occupies the narrow space 

 between the posterior area and the front margin of the valves. It is 

 widest in the middle and diminishes very gradually in size both above 

 and belo^v. The third, or posterior area, is much larger than the two 

 others combined and includes the whole of the shell behind the central 

 area. Two very faint, shallow grooves, with a small and equally faint, 

 linear rib between them, extend obliquely from the beaks to the middle 

 of the pointed base, and these together form the front boundai-y of the 

 posterior area and mark its separation from the central space. The 



