450 
Ohs. This genus is proposed to include two stells described by Mr. Moore as 
referable to Liicina, the characters of which are but imperfectly known to me ; neyer- 
theless, they are sufficiently clear to show that they cannot be referred to a so-called 
Dimyarian genus, but in all probability partake more of the nature of the Avicttlida. 
The genus must, therefore, be looked upon as, to some extent, provisional. 
Although I never understood Moore’s reference of his species to Lucitia, it was 
not until Mr. H. T. L. Brown forwarded a series of specimens to the Natural History 
Museum, London, from Coottanoonna, in South Australia, that I was able to satisfy 
myself that Lucina anomala and L. ? australis were not Lucincs, but a Monomyarian 
shell. 
Moore described both his species as nacreous, and this should have at once been 
sufficient to exclude these shells from the LuciniilcB. The separation into two species 
depended only on the presence in one of finer costm, and a less extended anterior hinge- 
line. The condition of the surface costm is perhaps duo to preservation ; and as regards 
the “ less extended anterior hinge-line,” the extended portion is posterior and not 
anterior, and the degree in this particular case is again to some extent a question of 
preservation. AVhen perfect the shells are decidedly inequilateral, and this at once 
does away with the mesial beaks. The only remaining Lucina character is the lunule 
said to exist in L. anomala, but I have failed to detect such a structure in the specimens 
examined by me. 
The point of view here advocated i.s supported by the nacreous character of the shell, 
the absence of hinge teeth, and the presence of a largo adductor muscle, which is shown 
in one of Mr. Brown’s specimens. The essential points in the genus, in addition to the 
general shape, are the absence of an anterior ear, the anterior margin being 
regularly and gently rounded; small byssal sinus; and the simplicity of the hinge 
mechanism. I am not acquainted with the latter as thoroughly as I could wish, 
but from the appearance of the cardinal margin in PI. 2i, fig. 12, the absence 
of teeth can safely be surmised. In all probability the valves were held together by 
a small external ligament and internal cartilage, placed in a groove, visible in the 
figure, as described by Iludleston. It is hardly necessary to point out that these shells 
are quite distinct from Avicula, as typified by A. hirundo, Linn. 
Type — Lucina anomala, Moore. 
PsEnnAVicunA anomala, Moore, sp., PI. 24, figs. 6, 8, 11. 
Lucina anmnala, Moore, Quart. Journ. Geol. Soc., 1870, xxvi., p. 251, t, 14, f. 4. 
Sp. Char. Shell suborbicular, generally compressed, thin, posteriorly alate ; valves 
slightly convex, flattened towards themargins. Dorsal margin short, straight on the posterior 
side ; anterior margin rounded below, abruptly cut off and o’oliquely rounded above ; pos- 
terior margin obliquely sub-truncate, entire posterior vving flattened, the angle ronnded. 
Umbones small but prominent; byssal sinus small, distinct. Sculpture consisting of a 
large number of very fine regular radiating cost®, becoming parallel to the dorsal margin 
on the wing, crossed by equally delicate concentric lines, broken up into broad bands 
or laminm, giving rise to flattened quadrangular spaces, the points of intersection 
becoming delicately serrate. 
Ohs. This species invariably occurs in large numbers matted and compressed, 
always presenting the same physical appearance, and invariably of the same size, 
seldom exceeding eleven-sixteenths of an inch in transverse measurement. I at one 
time took this and the following species to be one, but the constant uniformity in size 
and much sharper surface sculpture of the present shell compel me to retain them 
separately — at any rate, provisionally so. Moore speaks of his Lucina ? australis as 
