458 
MACCorKLLA. TJMBO^Atis, Moore, sp., PI. 22, figs. G-7, PI. 23, fig. 4. 
AviouJa umhonalis, Moore, Quart. Journ. Geol. Soc., 1870, x.'cvi., p. 246, t. 12, f. 2 and 3. 
Sp. Char. Shell large, transversely ovate, almost plano-convex, nearly equi- 
lateral ; dorsal margin long, straight, nearly equal on both sides the umbones. Left 
valve moderately convex, its umbo much produced, and incurved over the hinge-liue ; 
anterior, posterior, and ventral margins rounded, the first slightly obliquely so, especially 
above, leaving a well-marked byssal sinus ; anterior dorsal margin much crenulated, as in 
M. Barklyi. Eight valve more or less flattened, or slightly convex. llnige area of 
the left valve moderately large, intersected by the two transverse folds, one 
immediately posterior to the byssal sinus, the other below the umbo, leaving posterior 
to it the greater portion of a shallow triangular depression ; that of the right valve is 
similar, with folds corresponding to the depressions of the former. Adductor 
impression very large. Surface with a very large number of close radiating costic, 
crossed by equally numerous concentric lamins, the cost® on the right valve becoming 
almost subordinate to the lamin®. 
Obs. I have not seen anything approaching a jDerfect specimen of the left or 
convex valve of this species, although an im|iression and an excellent right valve exists 
in Mr. Sweet’s Collection. It is the lai-gest Maccoydla—a. mutilated left valve obtained 
by Prof. Tate at Lake Eyre, in South Australia, measuring four inches from anterior to 
posterior, and four anda-half inches from the dorsal to the ventral margin. Mr. Sweet’s 
right valve is six inches in transverse measurement, and five and a-half inches iu the 
contrary direction. I think there is little doubt also that our PI. 23, fig. 4, is this 
species, and represents an exfoliated right valve, with the umbo and crenulations of the 
left anterior dorsal margin perceptible above it. The impression of the left valve 
referred to above measures five inches in both directions. The radiating cost® are very 
numerous, and appear to extend beyond the ventral margin as spinous prolongations, 
to M. Barklyi, mariwburiensis (PI. 42, fig. 4). The costae are crossed by 
moderately wide growth-laminae, which, at the points of intersection, project as half- 
•spines or frills. 
The structure of the hinge in M. umhonalis is remarkably interesting, differing 
in some degree from that of itT. rejlecta, and paving the way for the structure of that 
of M. corbiensis. 
The large shell from Maryborough (PI. 23, fig. 4), apparently either much 
decorticated, or split in half, with the shelly layers remaining along the hinge-line, 
measures five inches by four and a-quarter, and there are still remaining indistinct 
traces of the radiating cost®. An imperfect specimen in the Mining and Gleological 
Museum measures six inches transversely from side to side, and four from the left 
umbo to the imperfect front or ventral edge. Another, still less perfect, from the 
Australian Museum Collection, is four and a-half inches by four. These measurements 
will show that M. refleota attained a large size. 
Log. Wollumbilla (The late Rev. W. B. Clarke) ; Pungeworgorai Creek, near 
Mount Abundance (O. Sweet — Colin. Sweet, Melbourne). Occurs also in the Mary- 
borough Beds — Desert Sandstone. 
MACCOYEimA coEBTEXsis, Moore, sp., PL 22, figs. 8 and 9. 
Avicida corbiensh, Mooro, Quart. Journ. Geol. Soc., 1870, xxxi., p. 246, t. 11, f. 7. 
Crenatula ? gibhosa, Etheridge, Quart. Journ. Geol. Soc., 1872, xxviii., p. 33!), t. 1!), f. 3. 
Sp. Char. Shell longitudinally ovate, longer than wide, somewhat deltoid, 
nearly equilateral. Loft valve very convex, longitudinally curved, area about 
one-third the width of the shell, much arched, with numerous fine ligamental 
