Tertiary. PALZONTOLOGY OF VICTORIA. [ Mollusca. 
PuatE XIX., Fias. 1, 2. 
TRIGONIA ACUTICOSTATA (McCoy). 
[Genus TRIGONIA (Brue.). (Sub-kingd. Mollusca. Class Dithyra. Order Pectinacea. 
Fam. ‘Trigoniide). 
Gen. Char.—Shell equivalve, inequilateral, subtrigonal ; outside ridged, inside pearly ; right 
valve, with a V-shaped pair of large diverging teeth, transversely sulcated on each side, received 
between 4 teeth, similarly suleated on one side, in the left valve. ] 
DescriptTion.—Rotundato-rhombic, moderately convex; posterior slope flattened ; 
anterior and ventral margins rounded, posterior margin obliquely sub-truncate, nearly 
straight, respiratory angle obtusely rounded, anal angle about 130°; surface radiated 
with about 32 acutely angular ribs, about 18 of which are on the posterior slope ; 
the intervening spaces seem wider than the ribs, from the sides of each rib gradually 
converging to an acutely angular line, closely set with numerous small thorny 
tubercles (about 7 in 38 lines at 6 lines from the beak); intervening spaces coarsely 
striated and wrinkled at right angles to the ribbing. Length from anterior to 
posterior end of average specimens, 1 inch 3 lines; proportionate width from beak 
to opposite point of ventral margin, ;°°;; depth of one valve, 3,95; length of anterior 
side, +0; length of hinge-line, =52,; of truncated posterior margin, 5%. 
Rererence.—Z. Lamarchi (Jenkins), Geol. Mag., v. iii., p. 201, t. x., f. 3-7 
(Not Math.). (McCoy), Geol. Mag., v. 3, p. 482. 
The genus Trigonia has hitherto been looked upon as an extra- 
ordinary and strongly marked exception to the usual geological 
law, almost universally observed, of the distribution of genera and 
species in Time, viz., that when a genus or species ceased to exist, 
by efflux of geologic time, it was never re-created, or never re- 
appeared at a more recent time than that of the formation in 
which it was absent. Now Trigonia is a very-abundant genus in 
the Oolitic and Cretaceous formations, but was unknown in the 
whole of the Tertiary periods in any part of the world, while it 
was well known to occur in the living state in the Australian seas 
of our time. Being enabled to announce the discovery of three 
distinct species of Trigonia from the Pliocene and Miocene Ter- 
tiaries near Melbourne clears away this supposed exception to a 
general Paleontological law, and cannot fail to be welcome, not 
only to geologists generally, but to the biologists engaged with the 
large question of the succession of life on our globe. 
The present species is easily distinguished even in fragments 
from the 7. Lamarcki, T. pectinata, and other recent species by 
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