SYNDOSMYA. 317 



a glossy, very thin, yellowish, and evenly spread epider- 

 mis, which is at times slightly opalescent ; the valves are 

 rather compressed, though not particularly so for this 

 genus, and their surface is nearly smooth. The sides are 

 distinctly unequal, the front exceeding the hinder by 

 nearly one half its length ; the ventral edge is simply arcu- 

 ated, and both the dorsal margins are more or less convex, 

 the front one but little sloping, the hinder one greatly de- 

 clining. The anterior extremity is rounded, but not broad- 

 ly so, the posterior end is obtusely angulated below ; the 

 umbonal ridge is entirely obsolete ; the beaks are small 

 and inflected, not leaning to either side ; the ligament is 

 very little, and often of a chestnut colour. The inside is 

 more or less nacreous and iridescent ; the cartilage-pit is 

 rather large, curved, and subtriangular upon the hinder 

 side just under the beaks, leans obliquely backward, and 

 contains a rufous orange-coloured cartilage ; the two late- 

 ral laminse are large, raised, approximate, and nearly 

 equal, their edges are slightly concave, and form an obtuse 

 or right angle near their termination ; the space between 

 their apices occupies one third of the entire hinge-margin. 



The measured length of a large Scotch specimen (the 

 northern far exceed the southern in dimensions) was very 

 nearly one inch, and its breadth was one third less : this 

 is at least one fourth larger than the size of any of our 

 English examples. 



The animal has very lately been submitted to a most 

 careful scrutiny by Mr. Clarke ; and, as his notes are 

 much fuller than our own, we draw from them the greater 

 part of the following description. It is compressed, sub- 

 ovate, and of a very pale bluish- white hue ; the mantle is 

 open, and very finely fringed with short filaments ; the 

 branchial and anal tubes are completely separated from 



