APPENDIX. 253 



Vol. i. p. 341. Ervilia oabtanea. 



Mr. Barlee has dredged living examples in ten fathoms water 

 at the Arran Islands, on the west coast of Ireland ; and Mr. 

 M 'Andrew has found the same interesting shell on the coast of 

 Spain. 



Vol. i. p. 354. Mactra truncata. 



The sight of a large number of magnificent Irish specimens in 

 the possession of Mr. Damon, has greatly unsettled our notions of 

 this supposed species. It must, we suspect, be referred to solida, 

 as an aberrant ventricose variety. The triangular outline, and 

 the projection of the beaks, which in certain examples are not 

 more oblique than in the typical solida, result from the greater 

 declination of the dorsal edges, which produce, of necessity, a 

 greater arcuation of the ventral margin. We believe it will be 

 found an invariable rule, that the relative proportions of the 

 dorsal and ventral edges are fixed in each species, but that consi- 

 derable latitude is permitted to the umbonal angulation. As a 

 natural consequence, the contraction of the angle at the beaks 

 must effect a corresponding increased curvature of the opposite 

 margin, since otherwise its length would be diminished ; and a 

 dilatation of the angle must produce an equivalent lesser degree 

 of convexity, or else that edge would not be long enough to meet 

 the dorsal extremities. The bow in archery, which becomes 

 curved in proportion to the angle formed by the drawn string, 

 will clearly illustrate our meaning. 



Vol. i. p. 370. LUTRARIA ELLIPTICA. 



Of this shell we have two very distinct forms ; the broad one, 

 which we have figured, and an elongated variety which approaches 

 in some respects to oblonga. In the former the dorsal edges are 

 usually more convex, and have a greater declination than in the 

 latter, where, for the most part, they are more or less retuse 

 towards the beaks. 



