2a2 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 
depressed; valves slightly convex; hinge-line on anterior side ex- 
tended and rather rounded ; margin of the valves regularly rounded ; 
surface ornamented by very close but distinct longitudinal costze. 
This shell may be distinguished from the L. anomala by the coste 
being finer; and although it is larger, the anterior hinge-line is less 
extended. “Its surface, “under the ‘lens, presents a wrinkled appear- 
ance, probably indicating the presence of fine concentric lines of 
growth which have been obliterated. It exhibits broad concentric 
bands. 
Loc. Wollumbilla. 
41, Macrra Trigonatis, sp.n. Pl. XIV. fig. 6. 
_ Shell small, thin, trigonal; umbones rather anterior; anterior 
end rounded and rather angular; front margin rounded; the sur- 
face is marked by faint transverse lines. 
A thin slab from the Downs on the Nive river, appears to be 
almost composed of this little shell. One species of the genus is re- 
corded by Professor M‘Coy from Carboniferous strata, and another is 
described from the Greensand ; otherwise the genus is chiefly met 
with in Tertiary deposits. 
42. Myritus ruco-costatus, sp.n. Pl. XIII. fig. 2. 
Shell thick, ovately oblong; umbones terminal and acute ; pos- 
terior margin ‘oblique and curved ; anterior side produced and some- 
what rounded ; the dorsal surface is obtusely keeled, and towards the 
umbo has very coarse irregular concentric strize or lines of growth, 
which become finer towards the ventral margin. 
Unlike the Mytilide generally, whose shells are usually thin and 
fragi'e, this species possesses a very thick test, especially in the adult 
examples. When a portion of the test has adhered to the matrix, 
leaving an inner layer exposed on the shell, the strize are not seen, 
and the surface appears smooth, giving it the appearance of an 
entirely different species. 
It is from Wollumbilla, and appears to be frequent. 
43, Myris PLANUS, Sp. n. Pl. XIII. fig. 3. 
Shell small, thin, ovate, compressed, nearly equilateral ; umbones 
terminal and acute, ventral margin rounded; dorsal surface smooth, 
with depressed concentric lines of growth, crossed by very fine radi- 
ating lines, which wholly co-er the exterior. Its flattened form, with 
its distinct ornamentation, readily distinguishes the species. 
I have only seen one specimen, which is from Wollumbilla. 
44, Myrinvus inFnatus, sp. n. Pl. XIII. fig. 4. 
Shell smooth, slightly inequivalve, convex, both valves inflated ; 
margins close-set; umbones terminal, acute, anterior; hinge-line 
extended and oblique; posterior margin and front rounded; dorsal 
surface smooth, with irregular concentric bands of growth. 
This pretty little shell is to be distinguished by its very inflated 
appearance, its more extended hinge-line, and terminal umbones. 
Its test still retains some colour, 
