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Dimensions. — The length is seven and a half, the breadth four and a 
half, the thickness three, and the distance between the beaks and the anterior 
margin three centimetres. 
Delations and Differences. — The internal structure, especially the 
muscular impression, resembles that of some species of SanguinoUtes ; but 
they are easily distinguished by the fact that as the tests of the SanguinoUtes 
are very thin, all the external ornamentation is reproduced on the internal 
casts, which is not the case with Clarkia. 
Jlorizon and Locatities. — The two specimens which have served me 
for this description, and which fortunately represent the two valves, come 
from a greyish sandstone at Wollongong, in which Mr. J. Dana also found 
the specimen he has figured. 
Genus — OARDIOMOPtPHA, L. G. de Koninck. 
Caediomoupha geyphoides, L. G. de Koninck. 
PI. XVIII, Pig. 1. 
This shell is tumid and globose, and remarkable for the form and 
size of its beaks, each beak being so strongly recurved as to meet itself. I 
unfortunately know only the anterior half of the shell, and its internal cast ; 
this fragment has, however, enabled me to discover the characteristics of the 
genus, and to assure me that it differs from those of its congeners already 
described. The internal cast has preserved the impressions of the anterior 
adductor muscles ; they are perfectly circular and very shallow. 
Dimensions. — The breadth is 7'5, the thickness six centimetres, and 
the length unknown. 
Horizon and Localities. — This fragment was found in a brownish 
sandstone near Stony Creek. 
Caediomoepiia ? STEiATELLA, L. G. dc Koninck. 
P]. XX, Pig. 3. 
Tliis is a small, oval, regularly ventricose shell, about one-third longer 
than broad. Its beaks are very small, slightly recurved, and placed nearly 
in the middle of the liinge line. The whole surface is ornamented Avith fine, 
concentric stride of growtli, scarcely visible to the naked eye. 
