Upper Silurian.] PALAZONTOLOGY OF VICTORIA. [ Mollusca. 
Pirate XLVI., Fias. 2-5. 
TREMATOSPIRA LIOPLEURA (McCoy). 
[Genus TREMATOSPIRA (Hatt). (Sub-kingd. Mollusca. Class Palliobranchiata, Order 
Brachiopoda. Fam. Spiriferide.) 
Gen. Char.—Hinge-line shorter than the width of the shell; cardinal angles rounded ; 
receiving valve with slightly produced or incurved beak, truncated by a small round perforation, 
separated from the hinge-line by a deltidium; no cardinal area; beak of entering valve 
received into a triangular pit under beak of receiving valve, as in Pentamerus. Teeth, sockets, 
and spiral apophyses as in Spirifera. Surface longitudinally sulcated. Texture fibro-punctate.] 
Descrrprion.—Orbicular when young, transversely oval and deeply bilobed when 
adult by a very deep, obtusely rounded sinus, scarcely raising the margin; both 
valves moderately convex, entering valve most so. Entering valve with eight 
simple ridges on each side of two slightly larger middle ones, which after 4 lines 
in length dichotomise so as occasionally to form four faintly marked mesial ridges 
not toothing the margin; after about 5 or 6 lines in length the lateral ridges 
suddenly become obsolete, leaving a broad, round, expanded, smooth, lateral margin 
on each side, marked only by concentric waves of growth, the mesial ridges only 
reaching the margin from the great depth of the scarcely raised mesial sinus. 
Receiving valve with reflected lateral margins when old, and a very deep rounded 
mesial hollow prolonged in front into a prominent tongue-shaped lobe, which fills 
without elevating the sinus in the opposite valve. About nine or ten lateral ridges, 
and about four faint mesial ridges at the end in old specimens, due apparently to the 
subdivision of one mesial ridge of the first 5 lines in length. In very old specimens 
the lateral ridges bifurcate. Length of receiving valve, 7 lines. ‘Texture coarsely 
granulate or fibro-punctate under the lens. ‘There is a moderately long mesial 
septum and two short diverging impressions of the base of teeth or apophyses in the 
small valve, and two small teeth in the opposite one or converging dental lamelle ; 
the apex of the beak is perforated. Apical angle, 110°. 
Young specimens slightly approach the young Hemithyris 
diodonta in appearance, but the lateral ridges are more numerous, 
and the two mesial ridges of the entering valve not so much 
elevated nor so obviously larger than the adjoining ones, while 
the broad, smooth, or unridged, bilobed margins or sides of the 
adult give a strongly distinctive character suggesting the specific 
name. The mesial hollow in the entering valve differs from that 
of H. diodonta in having about four faintly marked ridges as thick 
as those of the sides. When large, the lateral ridges, as well as the 
mesial ones, branch, which those of H. diodonta do not usually do. 
[ 21 ] 
