FOSSILS OF NEW SOUTH WALES. 699 
47. Nucuta concinna (Dana).—Plate 7, fig. 4, an imperfect specimen, natural 
size.—We thus name a small delicate species, of which we have but an imperfect speci- 
men. It has a smooth exterior with occasional lines of growth, and the valves thin. 
The form is oblong ovate, subacuminate and thinning much behind; length nearly twice 
the height; surface not at all carinated posteriorly ; apical angle nearly 150°.—From 
Harper’s Hill. 
48. NucvuLa GLENDONENSIs (Dana.)—Plate 7, fig. 5. A compressed specimen, natu- 
ral size.—This is another species which we characterize from an imperfect individual, 
the specimen being much flattened. Shell quite thin, short subelliptical in form, broadly 
arcuate behind; dorsal margin straight; anterior margin nearly at right angles (about 
100°) with the dorsal. Length half an inch; breadth two-thirds the length. One valve 
is slightly convex; the other through compression is concave. From Glendon, 
Genus EURYDESMA.—This genus was instituted by J. Morris, Esq., for a species 
from Australia, referred doubtingly to Isocardia by J. D. Sowerby. | He considers it 
near Avicula in essential characters, and describes it as “ equivalve, suborbicular, thin, 
but thick at the umbos; ligamental area elongate and almost wholly internal; a large 
obtuse tooth in the right valve, none distinct in the left; a byssiferous canal passing out 
of the umbos at the margin of the shell; several small muscular impressions, situated 
within anteriorly beneath the umbos, (‘ex internam partem umbonis.’)” 
Our collections contain several specimens and two or three species; yet it is difficult to 
lay down, with certainty, all the characters. The species are evidently inequivalve, 
subequilateral, with the beaks approximate, incurved, and curving a little forward; the 
left valve, under the beak, is very much thickened, and the hinge line is consequently 
bent far to the right, as shown in the figures; the valves are very thick beneath the 
umbos, as is shown in figure 8 d, which is a transverse section of a valve across the 
beak, the outer or lower part of the valve being wanting. In this species, about three 
inches high, the thickness at the beak is nearly an inch and a quarter. The hinge in 
the left valve is simply a broad waved surface, with a depression somewhat anteriorly, 
answering to a large rounded prominence or tooth in the other valve, as described by 
Morris. The inner surface, of which we have a good specimen, is rather finely and 
irregularly pitted, without any of the prominences represented in Morris’s first figure on 
plate 12; instead, there are below the beak two small depressions half an inch apart, as 
shown in figure 8 e, and supero-posteriorly there are four smaller pit-like depressions 
forming a curved line, half an inch long. These depressions have a very similar posi- 
tion and appearance to those of the common Meleagrina, and are undoubtedly for mus- 
cular attachment. Other muscular impressions are not distinguishable in our specimens, 
and no palleal impression. ‘There are some analogies to the shell of a Hippopus and 
also to that of a Meleagrina. In one fine specimen, in which the beak of one valve is 
broken half off, there is a tubular cavity (filled with rock) coming up obliquely from 
between the beaks and passing out anteriorly ; and this cavity was probably the byssi- 
ferous channel. 
