220 GO^GRYLIA—DITHYRA. 48. 



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

 sus which issues from a sinuosity or notch near the base of the un- 

 der valve. We have examined a small living specimen attached to 

 the Gorgonia virainalis. 



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 anterior 

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

 the end, as is rejiresented in Chemnitz, viii. tab. 81, fig. 723. 2, 

 where the tail is about as long as, or reaching parallel with 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, 



Hirunilo. AvicULA caudd longitudine ala. 



With the tail as long as the wing. 



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

 Mytilus Hirundo. Linii Syst. Nat. p. 1 159. 



Gmelin, Syst p. 3357. 



Turton, 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 and 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 brown 



