236 
at variable distances from each otlier, becoming wider apart as they recede 
from the beak. By this arrangement the surface of the valve looks like 
lattice-work. This small shell possesses a relatively large ligamentary area, 
two millimetres broad and fifteen millimetres Iona;. The beak of the riarlit 
valve is pointed and scarcely projects beyond the hinge line. The anterior 
ears are nearly rectangular at their extremities, and are completely separated 
from the rest of the valves by a curved furrow, which, in the left valve, 
terminates in a byssal notch. The posterior ears are much more developed 
and depressed ; they are prolonged into a sharp point the edge of which is 
united to the posterior edge of the shell by a very decided sinus. 
Dimensions. — The length and breadth are about thirteen millimetres, 
and the thickness four to five millimetres. 
Delations and Differences . — It differs from A. nohilis by the simplicity 
of its radiating ribs, by the smaller number of, and the greater distance 
between, the concentric folds. 
1 
Horizon and Localities. — It is found in Yorkshire at Settle and Bol- 
land, in Ireland at Little Island, in Belgium at Vise, and in Australia at 
Burragood. 
Aviculopecten proeunuus, L. G. de Koninch. 
PI. XXII, Pig. 3. 
This is a large, suboval shell, a little broader than long, with a very 
convex right valve. Its beak is slightly curved, rather sharp, and does not 
project beyond the hinge line. Its posterior ear is very large, terminates in 
a right angle, and is united to the rest of the valve by a broad sinus ; its 
surface appears to be smooth, and is certainly destitute of the radiating folds 
which cover the rest of the surface of the shell. These folds, numbering 
thirty or forty, are simple, subequal, slightly angular, and separated ])y 
shallow furrows grooved at the bottom ; this last characteristic distinguishes 
the species from A. 'planoradiahis, the folds of which are flat, and the 
furrows linear. LTnfortunately, I do not know either the left valve or the 
anterior ear of the species. 
Dimensions. — The length is seven, the breadth about eight, centimetres, 
and the thickness of the right valve about two and a half centimetres. 
