225 
Melaiions and Differences . — By its general form and its concentric 
striae, this species approaches T. {Nucula) attenuata, Eleming, hut it differs 
from it widely in its proportions, its breadth and thickness being so much 
greater in proportion to its length. 
Dorizon and Localities . — A single specimen of this pretty species was 
found in a greyish sandstone, in a railway cutting between Maitland and 
Stony Creek. 
Genus— VALMAiKQk, J. IlalV 
Bal^arca costellata, jP. McCoy} 
P). XVI, Fig. 6 and 7. 
Dyssoarca costellata, F. McCoj', ISIl, Synop. Carb. Foss. Ireland, p. 72, pi. 11, lig. 3(3. 
jLrca Lacordairiana, A. d’Oi’biguy, 1850, Prod. Pal., I, p. 131 (non L. Gr. de Koninck). 
,, costellata , ,1. Morris, 1851, Cat. Brit. Foss., p. 115. 
A rather small, elongated, subrhomboidal shell, with extremely convex 
valves, and very nearly twice as long as wide. The beaks are proportionately 
thick, and placed on the anterior third of the shell. The anterior side is short 
and rounded, the posterior truncated, and nearly rectangular, and the ventral 
margin subparallel to the hinge line. The two hinge teeth are posterior, 
elongated, and oblique to the hinge line. The surface is divided into two 
parts by an oblique keel beginning at the beak, and abutting on the angles 
formed by the intersection of the ventral and posterior margins. It is entirely 
covered by small radiating ribs of nearly equal thickness, crossed by concentric 
lines of growth of which the interior of the valve preserves no trace. 
Dimensions. — The length is eleven, breadth six, and thickness three 
millimetres. 
Delations and Differences. — This species is closely allied to P. 
Lacordairiana, de Koninck, with which Orbigny has confounded it ; it differs 
from it by its small size, by the less sinuosity of its ventral margin, and the 
greater regularity of its ornamentation. 
' [The specie .? — interrupta and suhargiita, De Kon. — are referred by Mr. R. Etheridge, Junr., to Area. 
Cat. Anstr. Foss., 1878. p. 62.— W..S.D.] 
- [Parallehdon costellata. R. Etheridge, Junr., Geol. and Pal. Q'land., 1892, p. 274, t. 40, fol. 12, 1.3. 
Mr. Etheridge suggests the possibility of the (Queensland form being a new species — Parallelodon Koninclci, Eth. 
fil.— W.S.D.] 
