220 CO^ CHY LI A— DITHYK A. 48. 



They inhabit the deeps of the ocean, and are attached by a 

 byssus which issues from a sinuosity or notch near the base of 

 the under valve. We have examined a small living specimen 

 attached to the Gorgonia viminalis. 



We are inclined to consider the genus, as far as it is yet known, 

 to possess three well-defined species : 1, where the tail, or ante- 

 rior elongated process is longer than the wing or body, and curved 

 at the end, as is represented in Chemnitz, viii. tab. 81, fig. 723. 

 2, where the tail is about as long as, or reaching parallel witli 

 the wing, as in our European species : and 3, where the tail is 

 shorter than the wing, or where the processes at the base are of 

 nearly equal length ; as is represented in Chemnitz, viii. tab. 81, 

 fig. 726. 



Hiruiido. AvfcuLA caudd longitudiiie alee. 

 With the tail as long as the wing. 



Tab. nost. 16, fig. 3 and 4. 

 Mytilus Hirundo. Linn. Syst. Nat. p. 1159. 



Gmelin, Syst. p. 3357. 



Tnrton, Linn. Syst. iv. p. 295. 



Dillwyn, Descript. Catal. p. 320. 



Turton, Conch. Diet. p. 108, fig. 7. 



Chemnitz, viii. p. 142, tab 81, fig. 724, 725. 

 Pecten tenuis. Lister, Conch, tab. 220, fig. 55. 

 Mus. nost. Dublin bay, Torbay, aud the western coasts. 



Shell nearly two inches long, and as much in breadth, including 

 the lobes, smooth or furnished with a few scales about the margin, 

 generally of an uniform dull greenish color, but sometimes brawn 



