TEREBRATULA. 15 



being the termination of the tubular perforations characteristic 

 of this family : colour yellowish- white: margins usually truncate 

 or square in front, and sometimes indistinctly notched or in- 

 dented in the middle ; the sides are rounded : beak prominent 

 but blunt, worn down obliquely by continual rubbing : fora- 

 men nearly round and incomplete below : deltidium very slight, 

 being interrupted by the point or umbo of the lower valve : 

 hinge-plate solid : teeth of upper valve as in T. cranium, but 

 thicker and provided with a sort of bolt at the upper end : 

 sockets in lower valve broad : skeleton consisting of two small 

 but stout ribs, which are thicker at the shaft near the outer 

 angle of the socket-joint, but afterwards become thinner and 

 broader or flattened out, forming a double loop or bow, the 

 upper one being nearly round, and the lower one of a trans- 

 versely quadrangular shape with a curve above and below ; 

 this complicated process extends about three-eighths of the 

 distance from the beak to the front margin ; within the lower 

 valve, beneath the umbo, is also a small tooth or tubercle ; 

 the inner margins are crenulated or slightly notched, with the 

 points projecting outwardly, and furrowed in the middle : inside 

 pearly and glistening. L. 0*85. B. 0-(35. 



Yar. septentrionalis. Shell thinner, with finer ribs, and of 

 a white colour. T. septentrionalis, (Couthouy) Stimpson, Test. 

 Moll. New Engl. p. 75. 



Habitat : 0-90 fathoms, on every part of the Scotch 

 and Shetland coasts, and on the north-east, west, and 

 south of Ireland, attached to stones, old shells, and occa- 

 sionally to small sea-weecls and other substances. The 

 variety occurs in Loch Duich, Inverness-shire, and off 

 the east coast of Shetland. This now common shell 

 was discovered in our seas by Professor Fleming, be- 

 tween forty and fifty years ago, in Loch Broom, on a 

 stone which was brought up by the anchor of a vessel 

 belonging to the Commissioners of Northern Light- 

 houses, while on their annual visit of inspection. As a 

 tertiary fossil it occurs in the glacial deposits of Ayrshire 

 (Geikie), and in the Coralline Crag (Searles Wood). 

 M. Drouet has noticed it as fossil in the Azores. Its 



