90 KELLIADiE. 



The hinge sometimes appears different, from there 

 heing- a very minute almost linear denticle, immediately 

 above the single tooth of the right valve, which, in 

 some specimens, becomes more developed, inducing 

 the idea of there being two primary teeth in each valve ; 

 and all these teeth frequently curve towards the beaks. 

 The internal surface, when slightly magnified, appears 

 a little punctulate, but does not exhibit any pallial 

 sinus. 



Specimens are usually about five-twelfths of an inch long, 

 and very nearly a third of an inch broad, but the propor- 

 tions are very variable ; we have seen none exceeding half 

 an inch in length. 



The fullest published account of the animal of this pretty 

 and Ci/clas-like shell is contained in Mr. Alder's valuable 

 catalogue of the Mollusca of Northumberland and Durham. 

 From this description, extensive manuscript notes commu- 

 nicated by Mr. Clark, and our own observations, we have 

 drawn up the following summary of its features. It is 

 white and translucent ; the mantle is closed, except at 

 three places, viz., in front or veutrally, where there is an 

 orifice for the passage of a narrow, long, slender, ligulate 

 foot ; anteriorly, where it is produced into a hyaline tube, 

 undivided within, very broad, and capable of extension to 

 a length equalling the breadth of the shell ; posteriorly, 

 where there is a single, very short tube or siphon, seldom 

 protruded beyond the shell. The margins of all these 

 orifices are plain, but there is a fringe of very minute, 

 short, distant, tentacular processes on the mantle, just 

 ^vithin the edge of the shell. The foot is furnished with a 

 byssal groove. The branchial leaflets are symmetrical and 

 subtriangular, the labial palps short, subtriangular, and un- 

 equal. When the animal is confined, as it often is, in the 



