61 
half an inch long/ Similar pits are described by Waagen in his E. elliptic urn. 
Hesays : — “Besides this large muscular impression there is a number of smaller 
hut much deeper ones, which are arranged in a curved line from the anterior 
part to near the apex, and from these again descending for a short distance 
in the direction of the posterior part. Towards the anterior region several 
of them are united, forming on the cast a high crenulated crest. Then 
follow, somewhat lower in position, three or four single ones. At the apex 
the line makes a sudden bend and then follows again one large impression, 
with which the whole series terminates, not far from the posterior margin of 
the large muscular impression described above.^ 
Idle surface of the lower or ventral margins of the hinge-plates in 
Meleagrina maxima. Jam., and Mallem malleus, Linn., are delicately 
crumpled transversely, and in more than one of our left valves of Eurydesma 
cordatum and in one of E. hohartense (Bl. XX, tigs. 2, 3, 5) the place of the 
crumpling is taken by a line of minute pits ; these occur on that portion 
of the hinge-plates corresponding to Lrech’s “ extended smooth surface ” in 
his Leiomyalina antarctica . 
10. Pallia, I Line. — This has never definitely come under our notice, 
hut is probably indicated by the dark semicircular outline seen in the internal 
cast of E. cordatum, var. ovale (PI. XXI, tig. 4). In the Pteriidse (Aviculidae) 
( — ) it is said to he irregularly dotted, but this is not the case in all members 
of the family — in Meleagrina maxima, M. margaritifera, var. Cwmingii, 
Pteria macroptera, &c., dotting or pitting is absent. 
11. Test. — ^The test or shell of Eurydesma was enormously thickened 
in the umhonal region, also in the hinge, and highly lamellate. The umhonal 
region consists of a solid mass having no umhonal cavity, as is tlie case in so 
many Pelecypoda — giving rise to a charaeteristic internal cast with truncate 
umhonal regions. Below the line of the hinge-jdate the test at first 
gradually and then rapidly decreases in thickness, until at the ventral 
margins it is comparatively thin. In some specimens the thickness through 
the combined hinge-plate and umhonal region attains to at least one and a 
half inches; in a specimen from Yatton, Q., a thickness of one inch has been 
recorded by one of us.^ 
* Dana in Wilkes — Op. cit., p. 699, PI. VII, fig. 8e. 
^ Waagen — Salt Range Fossils, toe. cit., p. 141. 
^ Etheridge — Geol. Pal. Q’land, &c., 1892, p. 277. 
