32 
of Prof. Tate’s paper, I was engaged in the study of the Cretaceous fossils of 
Queensland, collected under the superintendence of Dr. E. L. Jack, and 
had independently arrived at the same conclusion. This opinion Avas suh- 
seqnently conlirmed hy an examination of specimens in the collections 
of Prof. Tate and Mr. II. Y. L. EroAvn, made in the Lake Eyre Basin. 
It is remarkable that iiotAvithstanding the large nuniher of specimens in 
different states of preservation passing through my hands in this Avay, not 
one, so far as I can rememher, revealed any portion of the hinge structure, at 
any rate, in a form sufficiently tangible to aid in definite generic determination. 
Now, however, I have succeeded in exposing the right articulus and con- 
tiguous parts of a specimen in the Alining and Geological Museum, more or 
less perfect, and some very interesting points are re\"ealed, indicating an 
affinity to Isocardia. 
The articulus or hinge plate is thick and massive, and exhibits a blunt 
and nearly horizontal projecting cardinal tooth, a (PI. X, Pig. 2), a little 
posterior to the lunhonal apex, Avith, on either side, and a little ahoA'e it, a 
Avidc and open cardinal socket, the anterior h (PI. X, I’ig. 2), being directly 
in a line Avitli the lunhonal apex, and the concavity of the posteriori (PI. X, 
Eig. 2), tailing-otf obliquely along the hinge plate in a posterior direction d 
(PI. X, Eig. 2). Above the latter at the terminal end is a .sharp oblique 
thickening e (Pi. X, Eig. 2), of the hinge plate. The extreme anterior and 
posterior ends of the aMvc are defective, and in consequence the lateral teeth 
are not preserved. 
The details of the left vahm hinge plate can he studied hy means of a 
cast from that of the right. There are tAvo cardinal teeth and (PI. XI, 
Eig. 2), fitting into the sockets Avith corresponding indicators in the right 
vah"e, and a socket (d, to receAe the tooth a (PI. X, P’ig. 2), of the latter. 
Eurthermore, an obtuse thickening (PI. XI, Eig. 2), is developed to fill the 
concavily d (PI. X, Eig. 2), and above it is a groove (PI. XI, Eig. 2), to 
receive the sharp oblique thickening e (PI. X, Eig. 2), of the right A^alA'c. 
These features are all that can at present he made of the dental characters of 
this peculiar shell. Through the imjierfect state of the right Amlve, laterals 
cannot he distinguished, and CAen in the best internal east I have yet seen 
(PI. X, Eig. 1), these are not apparent. 
The prosogyrato umbo is much bent down at the apex, hut hardly 
inrolled, the ligament groove h (PL X, Ihg. 2), passing directly under it, 
as in Isocardia humana, Linn. {= I. cor, Linn, et auct.), and then posteriorly 
