455 
Maccotella Baeklti, Moore, sp. 
PL 22, figs. 1-5 ; PI. 42, figs. 4-6 ; ? PL 23, figs. 1 and 2. 
Avicula BarMyi, Moore, Quart. Journ. Geol. Soc., 1870, xxviii., p. 24.'), t. 11, f. 1-2. 
Streptorhpnchiis Daxidsoni, Etheridge, Ihid., 1872, xxviii., p. 333, 1. 17, f. 1. 
Monotis BarMyi, Tate, Trans. R. Soe. S. Australia, 1885, vii., p. 76. 
Sp. Char. Shell sub-orbieular, sometimes irregularly or slightly obliquely 
so ; test thick ; valves phmo-couvox, or slightly bi-eonvex ; hinge hardly as long as the 
shell ; ventral margin rounded. Posterior wing more or less flattened in the right 
valve, and much larger than in the left, where it is sharply cut off by an umbonal 
ridge; posterior margin usually rounded and graduating into the ventral. TJmbones 
very unequal ; in the right valve small and inconspicuous; in the left prominent and 
blunt, projecting above the dorsal margin, but not greatly overhanging it. Scar of the 
adductor large in the right valve, nearly central, sub-reniform in outline ; a deep pit is 
present behind the inflected portion of the cartilage area, and united to the adductor 
scar by a scries of muscular pits arranged in a semicircle. The radiating costae of the 
left valve are strong and prominent, from nine to thirteen in number, but fewer than 
those of the left; the posterior costa, and sometimes others, stronger and larger than the 
others, and bearing strong projecting spines ; intercostal spaces with a secondary costa 
between every pair of primary costm ; the right v.alve bears a largely increased number 
of costas ; in both valves are several broad concentric laminae of growth, but in the 
right those become elevated on the anterior dor, sal margin into prominent undulating 
ridge-like folds. 
Ois. Mr. Moore stated that sections of this shell were to be found in almost 
every block of matrix from Wollumbilla examined by him, a fact I am able to confirm 
from independent observation. Tt is also true that 21. BarMyi possesses a much 
wider geographical range than was at first contemplated by its describer. Furthermore, 
it is one of the most important shells, from a stratigraphical point of view, met with in 
the U pper Mesozoic Eocks of Eastern Australia. 
The surface cost® in 21. BarMyi, although varying in individuals to some 
extent, are characteristic, but this variability may perhaps have some relation to the 
state of preservation of the specimens. The left valve bears from nine to twelve * or 
6Ton thirteen sharp, separate, and prominent ribs, usually alternating with an equal 
number of finer secondary ribs which stop short of the umbo by some little distance. 
lEe posterior wing is free of cost® and separated from the body of the valve by the 
most posterior principal costa, which takes the place of an umbonal or diagonal ridge 
in the higher bivalves. The secondary cost® are sometimes increased to two, or even 
three, between each pair of primary, but the latter number is rare. The whole valve 
is concentrically crossed by well-marked laminar imbrications, the points of intersection 
with the primary cost® projecting as spines (PL 22, fig. 3; PL 42, figs. 4 and 5), 
especially in young individuals ; but in more mature individuals these projections 
become worn down, and are retained in some cases only on the last posterior, the pen- 
ultimate, and the anti-penultimate cost®. The presence of these spines gives to 
the fossils much the appearance of the genus Plagiostoma. One peculiar fact in con- 
nection with the concentric lamin® is the manner in which they pass over the anterior 
dorsal margin as ridge-like folds (PL 22, fig. 2 ; PL 23, fig. 4), and there is reason to 
believe they are conterminous with some of the cartilage furrows of the anterior 
area. 
* In one case only six were observed. 
