APPENDIX. 249 



internally, clearly shows its subnacreous structure ; a slight 

 linear ridge runs from near the beaks behind the front scar : the 

 ventral edge is slightly yet decidedly convex. The pallial sinus 

 is not perceptible in any of the specimens ; the lateral muscular 

 scars are well impressed, particularly the conical front one, and 

 both of them are seated high up. 



Of our British shells the nearest approximation to this hinge 

 is found in Thracia distorta, and how far individuals of that 

 polymorphous species, when not imbedded, may approach it in 

 shape, we cannot say. One might be tempted to imagine it the 

 Mytilus plicatus of Montagu and Laskey, said to be found at Skye, 

 but neither its delineation nor the affirmed angularity of its 

 broader extremity answers to the characteristics of our shell. 

 Notwithstanding that we cannot identify our specimens with any 

 described shell, we shrink from the responsibility of naming a 

 species whose specialities have only been observed by us in a 

 single valve^ and some very immature individuals. 



Vol. i. p. 174. Panop^a Norvegica. 



Mr. Kichard Hovvse has obligingly communicated a drawing of 

 the animal of this rare shell, with the following description drawn 

 up by Mr. Clark. 



" Animal oblong, thick. The branchiaD are extensive but not 

 deep, well arcuated on the body, the upper one lapping about 

 half on the surface of the under one ; they are very long, and 

 after quitting the body they gradually taper, becoming linear, 

 and are prolonged to nearly the extremity of the siphonal appa- 

 ratus, terminating in sharp points. The tube is at least seven 

 inches long, and the branchire cannot be much less. On the 

 body part of them the pectinations are visible, but not strong ; 

 and on the same portion, the colour is drab, aspersed rather 

 sparingly with minute bistre-coloured points. The palpi are 

 long, slender, delicate, pointed, and triangular, united around 

 the mouth, pale drab, smooth without, and finely marked within. 

 The body is of a rather thick oval mould, pale pinkish drab ; 

 from its centre a very small byssal-grooved foot proceeds, which, 

 as far as I could judge, would, when exserted, resemble that of 

 Gastrochcena or Saxicava and certainly be less linguiform than 



VOL. IV. K K 



