452 
the left or convex valve the hinge area is shorter, wider, and triangular under the 
umbo, and is divided more or less distinctly into two ill-defined cartilage concavities, 
separated by a rather prominent ridge ; the folding of the hinge of the right valve gives 
to it the appearance of possessing a deeply separated and lobate small anterior ear. In 
the left valve the anterior ear is not defined from the body of the shell, but is repre- 
sented by a corrugated thickening of the hinge. Adductor impression very large. 
Surface bearing radiating costae, more numerous on the left valve, delicate concentric 
striae, and concentric growth-laminai, the points of iiiterseetion being sometimes spinose. 
Ohs. I have much pleasure in proposing this genus in honour of Professor Sir 
P. McCoy, of Melbourne, taking for the type species Moore’s Avicula BarJehji. 
It is hardly necessary to mention that the shells included by the late Mr. Moore 
in Avicula do not in any way correspond to that genus, as restricted by Lamarck, and 
typified by the well-known Avicula hirundo, Linir. In the Queensland shells there is 
an entire absence of the narrow extended posterior wing, deeply emarginate posterior 
end, and the small pseudo-cardinal teeth of Avicula ; but, on the other hand, there is 
a much greater inequality of the valves and a peculiar hinge mechanism quite foreign 
to the genus quoted. 
The chief peculiarities of Maccoyella lie in the structure of the hinges of both 
valves. In the right valve of the type species and UL. refltcia there is a broad and 
strong area, with many longitudinal cartilage furrows, the course of which is inter- 
rupted by a strong inward inflection, or fold of its substance, having much the 
appearance of a small lobate ear, and in addition giving rise to a narrow but deep 
byssal sinus. It does not, however, appear to partake of the true nature of an auricle. 
The fold is well shown in PI. 23, figs. G and 7, and the false ear in PI. 22, figs. 4 and 5, 
and PI. 23, fig. 2 ; but it will bo observed that the cartilage furrows are continuous 
along the whole length of the area (PI. 23, tig. 7). 
In the convex or left valve the area is similar, but in addition somewhat 
triangular under the umbo, and there would appear to be two depressions in which 
thickened poortions of the cartilage, or plugs, were inserted. 
The umbo in the left valve is prominent, convex, and overhangs the hinge to 
some extent, but it is not usually inrollod. In the right valve it is insignificant. The 
muscular impressions ai’e only known in the type, and will be found described under 
that species. 
Avicula Barklyi, Moore, approaches more closely to Meleagrina, Lamk., especially 
in the convexity of its valves, broad cartilage area, form of the posterior wing, deep 
byssal sinus, and the small cleft pseudo-ear of the left valve. On the other hand, the 
size of the right umbo i.s quite unlike that of Avicula inargaritifera, Linn., the Mother- 
of-Pearl Oyster, and type of the genus Meleagrina, not to mention the inflection 
of the cartilage area. The tumidity and prominence of the right umbo wmuld appear 
to iudicate a relation to Oxyioma, Meek, typified by Avicula Munsteri, Bronn, but the 
posterior wing and byssal notch differ so widely from those of Moore’s species that 
they can hardly be congeneric. 
I am sorry to be unable to agree with so distinguished an authority as Prof- 
E. Tate in referring the shell now under discussion to the genus Monotis, Bronn. 
The latter, as represented by M. salinaria, Bronn,* is au ovate compressed shell, almost 
equivalve, with the beaks only slightly projecting, and in no way whatever resembling 
Moore’s species. The same remarks apply to other allied genera, such as Salobia, 
Bronn, and Baonella, Mojsisovics. None of the genera previously mentioned possess 
Jahrb. fur. Min., 1830, p. 284, t. 4,_£. 1. 
