KELLIA. 95 



umbonal fold or ridge ; the beaks are touching, prominent, 

 but very blunt, and do not apparently lean to either 

 side ; the umbones themselves are very wide. The sides 

 are unequal ; the posterior occupying at least three-fifths 

 of the entire length. Both sides are rounded at their 

 extremities ; the hinder, which is very slightly tapering, 

 the more regularly ; the front, which is likewise the 

 broader, the more obtusely so. The ventral edge is simply 

 and distinctly arcuated ; the front dorsal margin is short, 

 straightish, and but moderately sloping ; the hinder dorsal 

 edge scarcely declines at all, but is straight near the beaks, 

 and then more or less arcuated. There is no lunule, nor 

 any trace of one. The colour of the interior, which often 

 exhibits a resinous gloss, is usually deeper than that of the 

 exterior ; the hinge-margin is almost invariably stained 

 dark purplish red, and the margin is perfectly entire and 

 closed all round. The dentition of the right valve consists 

 of a very small sharp central tooth and a rather larger 

 widely diverging one just behind the apex ; the anterior 

 hinge-margin is extraordinarily thickened in both valves, 

 forming- a broad but shallow bed for the elongated carti- 

 lage that runs along the inner edge of it, which slopes 

 inwards. The other valve contains a rather approximate, 

 small anterior lateral tooth, and an oblique tooth-like 

 laminar elevation of the hinge-margin (which is not (infre- 

 quently surmounted near its commencement with a minute 

 apical denticle) just behind the apices. Specimens at all 

 worn, or when examined with a lens of low power, only 

 exhibit a broad hinge-margin with a wide triangular 

 excavation just beneath the apices of the shell. 



The average length is about the seventh of an inch, and 

 the breadth is nearly a quarter less. 



Minute as this shell is, its animal has not escaped 



