NE^RA. 197 



small sunken receptacle which Inclines hindvvard, and 

 seems generally to project more below the surface of the 

 hinge-margin in the left valve than in the right. There is 

 but a single tooth, namely, a very large and elongated 

 approximate lateral one, which is laminar and trigonal : 

 it is situated on the posterior side, and leans inwardly with 

 the apex curving again outwards and upwards. 



There are two very distinct varieties ; the one which is 

 the more frequently obtained has the rostrum remarkably 

 short, and the ventral edge peculiarly bulging out ; the 

 other, which we have only received from Loch Fyne, has 

 a much more produced rostrum, and a far more slender 

 shape altogether. It is from the latter then, which is 

 connected with the former variety by imperceptible grada- 

 tions, that we consider the identity of our species with that 

 of the Mediterranean to be established. Olivi's original 

 figure is somewhat rude, indeed ; but, making allowance 

 for the inaccuracies of engraving at that period, sufficiently 

 coincides with our specimens : Risso's rough drawing is not 

 an uncharacteristic representation of the ordinary and larger 

 form. 



Animal white, mantle united except for a space ante- 

 riorly, Avhere a white lanceolate foot is jirotruded. Siphons 

 short, united, the branchial largest and longest, tawny 

 with reddish dots. From the anal is protruded a slender 

 pellucid lancet-shaped tube, or veil, with two bright-red 

 dots at its base. These marks are between and among three 

 white filamentary cirrhi with lobed extremities. Four 

 similar organs are placed at either side of the branchial 

 siphon, and all appear to spring as it were from a split 

 sheath. 



As a native of Great Britain, the merit of the dis- 

 covery of this curious and interesting shell is due to Mr. 



