90 
the furrow I have just mentioned; sinuous strise, parallel to the lateral 
border and formed by the periodic growth, cross these ridges obliquely. The 
posterior ear seems to have a slightly greater extent than the anterior, and is 
separated from the rest of the valve only by a feeble oblique depression ; its 
surface is ornamented with small, rather close, curved striae. 
Relations and Diff erences. — I know no Devonian species that can be 
confused with that I have just described. In its ornamentation it resembles 
A. leiotis and micropterus, McCoy, which are Carboniferous species, but which 
differ from it in size and general shape. 
Dimensions. — Length, about four centimetres ; width, forty-three 
millimetres. 
Horizon and Localities . — This pretty species, which I have dedicated 
to Mr. D. Etheridge, whose work on the fossils of Queensland I have already 
had occasion to mention, has been collected by Mr. Clarke in the black 
argillaceous limestone oE the Yass District, Its shell is silicified, as is the 
case in most of the other species occurring at the same locality. 
2. Aviculopecten Clarkei, L. G. de Koninch. 
PI. Ill, Pig. 10. 
As in the preceding species, I am acquainted with only one valve of 
this shell — that is, the left — which is of moderate size, a little longer than 
broad, and the beak is rather pointed, its angle measuring only 85°. The 
ventral margin is fairly uniformly rounded and blends with the lateral 
margins by a regular curve. The surface is ornamented with ten to twelve 
radiating ridges about a millimetre thick towards the margin, and interrupted 
here and there by slight inflations that appear to me to have been the base of 
imbricating lamellae. At some distance from the apex sharp thinner ridges 
arise by intercalation between the primary and like those continue towards 
the margin. The ears, which probably were rather small, are quite unknown 
to me. 
Dimensions. — Length, twenty-two millimetres ; width, twenty milli- 
metres. 
Relations and Differences. — In the ornamentation that covers its 
surface, its size, and general form, this species has much resemblance to 
