222 
and snb-cordiform. The external ornamentation is remarkable ; the anterior 
part, forming nearly one-third of the total surface, is covered with small 
wrinkles, parallel to the ventral margin ; while the posterior part is 
crossed obliquely by from twelve to fifteen radiating ribs, the central one 
coming from the beak ; these ribs, perfectly distinct from each other and very 
much alike, are crossed by minute, scarcely perceptible strise. According 
to Mr. Morris the muscular impressions are rather strong, and are united by 
a simple pallia! impression. I was obliged to change the name given it by 
this learned geologist, because Brown had already made use of it for an 
entirely different species ; but I have taken the opportunity to dedicate it to 
him. 
Dimensions. — The length is eight, and the breadth one and a half 
centimetres. I have taken these measurements from the figures published 
by Mr. Morris. 
Relations and Differences. — According to Morris this species bears 
some resemblance to Cypricardites corrugata, Conrad. 
Sorizon and Localities . — It was found in the Illawarra District by 
Strzelecki, and in a greyish sandstone at Wollongong by the Bev. W. B. 
Clarke. 
Pleurophorus biplex, L. G. de Koninch. 
PI. XIX, Fig. 1.' 
This is a moderate sized, elongated, elliptical, rather thick shell, having 
its hinge line and ventral margin sub-parallel, its anterior and posterior sides 
rounded, and its beaks very anterior and thick. Judging from the traces 
preserved on the only internal cast sent me the external ornaments were 
concentric striae, and two oblique ribs starting from the beak and dividing 
the surface into two, nearly equal, sub-triangular parts. This arrangement 
leaves no doubt as to its generic determination. The impressions of the 
anterior adductor muscles are small, sub-triangular, and longitudinally 
wrinkled. I could not find the posterior muscular impression. 
Dimensions . — The length is forty-five, the Ijreadth twenty- one, and 
the thickness seventeen millimetres. 
‘ [PI. XIX, fig. 7.— W.S.D.] 
