FOSSILS OF NEW SOUTH WALES. 695 
Pyram1a.—No accessory muscular impression anteriorly. Lateral surface more or 
less compressed (observable at least in the cast). Palleal impression distinct or indistinct. 
A cast of the hinge of a left valve is well preserved in two of our specimens belonging 
to two species, which we had referred to this division; and it is possible that when the 
hinge in other species is made out, a more decided separating line may somewhere be 
satisfactorily drawn, There are no distinct teeth; the cast has a low, oblong, obtuse, 
subtriangular prominence, directly under the beak, with an oblique sulcus on its posterior 
side; in front, a shallow depression, prolonged and diminishing forward; and behind, an 
oblong depression, slightly deepening, and then diminishing again. Figures 4 c, and 6 a, 
plate 6, represent the form of the cast of the hinge, in the two specimens referred to, 
Cieosis.—No accessory muscular impression anteriorly. Lateral surface not at all 
compressed. Beaks a little salient, and projecting over the cardinal area. Valves thin. 
Palleal impression faint. 
The genus Notomya of M’Coy corresponds to our Pyramza, and was subsequently in- 
troduced. It is considered by M’Coy as having a relation to the Myidee, but there is no 
true sinus to the palleal impression, and besides, they have two anterior muscles; the 
resemblance appears to be only in external form. 
35. Mmonra ELoneata (Dana).—Thick ; very inequilateral, oblong, length twice the 
height; narrowing behind. Right valve slightly highest. Sides obliquely excavate ; 
rounded carinate posteriorly, with the flanks flattened, and slightly bending; inferior 
margin a little excavate along the middle. Exterior surface strongly concentric striate, 
and large. Muscular impressions with vertical erosions. A small accessory muscular 
impression on the front of the beak.—Length 63 inches ; height $5 L.; thickness 42, L., 
or °°, H.—Plate 5, fig. 3 a, , c, views, natural size. 
Black Head, District of Illawarra. 
This species has not the flank strongly bent like the following, and is much longer 
in proportion, and less rapidly narrowing behind. ‘The anterior part is less than one- 
third the whole length. 
Myonia elongata, Exped. Foss., Amer. Jour. Sci., 11. ser., lv. 158. 
36. Mzonta vatipa (Dana).—Thick; very inequilateral, oblong, length somewhat 
less than twice the height, rather rapidly decreasing in height, posteriorly and obliquely 
truncate behind, strongly carinate, with the flank (in cast) flat and broad, and bent at the 
posterior muscular impression. Left valve slightly highest. Sides obliquely excavate, 
inferior margin excavate. Large muscular impressions with strong vertical erosions ; 
the larger anterior produced upward nearly to smaller anterior. Accessory muscular 
impression on front of beak. Palleal impression very strong, with delicate vermiform 
erosions running upward from it, and others (attachment of muscular fibres) scattered 
over the lateral surface.—Length of cast 6 inches ; height zoo L.; thickness 545, L. ; apical 
angle of cast 128°.—Plate 5, fig. 4, a, 6, views, natural size. 
Black Head, District of Illawarra. 
We have only a cast of this species. The anterior part is less than one-third the whole 
length. 
Myonia valida, Exped. Foss., loc. cit., p. 158. 
