12 TEREBRATULIDjE. 



complete at the lower end : deltldium (or triangular space be- 

 low the beak) slight, and divided by the point of the lower 

 valve: lunge-plate of both valves exceedingly thick, forming 

 strong supports for the teeth and lamellar processes ; from 

 these processes extend into the interior two diverging ridges 

 or septa in the upper valve, and three or more in the lower 

 valve : teeth of upper valve very strong and projecting towards 

 each other : sockets in lower valve deep : skeleton consisting 

 of two thin and elastic blades, which reach within about one- 

 fourth of the front margin j they are furnished with upright 

 spurs at a short distance from the hinge -plate, and have sharp 

 points. L. 1. B. 0-8. 



Var. ohlonga. Shell much narrower and deeper than usual, 

 and having the front margin nearly straight. 



Habitat : Rocky and stony ground, from 50 to 90 

 fathoms, on the north and east coasts of Shetland, but 

 exceedingly rare in a living state. More than fifty years 

 ago, when the late Professor Fleming was Minister of 

 Bressay Island, a stone was brought to him by one of 

 his parishioners, a long- line fisherman, to which three 

 specimens of this curious shell were attached. One of 

 them was sent to Col. Montagu, who described it in the 

 eleventh volume of the ' Linnean Transactions/ My 

 late friend Mr. Barlee, as well as myself with Mr. Wal- 

 ler and Mr. Norman, have lately dredged specimens of 

 various sizes and ages in the same part of our seas, at 

 distances from land ranging from one to thirty-five miles. 

 The locality ("Dublin Bay"), recorded by Dr. Turton 

 in his ' Conchological Dictionary/ appears to be more 

 than questionable, especially as he omitted it in his sub- 

 sequent work on the British bivalves. This species 

 does not appear to have been found in any of our upper 

 tertiaries j but, in all probability, the T. euthyra of Phi- 

 lippi, a fossil from a corresponding formation in Sicily, 

 is the same species. T. cranium is rather common on 

 the Scandinavian coasts; and Dr. Wallich obtained dead 



