et oe 
characteristic of Tertiary Beds near Melbourne. 437 
ridges, faintly indented with transverse, broad, scarcely visible 
marks ; the ridges are usually interrupted by a narrow, shallow, 
longitudinal, depressed, smooth space along the middle of the 
back ; five, six, or seven pass vertically over the spiral whorls, 
and on the inner lip they are inflected angularly at the edge of 
the aperture to form a concave inner lip as wide as the mouth, 
and terminate in tubercles on its inner edge; the dorsal ends 
not swollen, sometimes, though rarely, joing from each side, 
effacing the dorsal sulcus, which, when present, varies irregu- 
larly from half a line to a line in width im a specimen of the 
ordinary size of 10 lines. Greatest length of very large speci- 
men, from anterior canal to most posterior part of outer lip, 
1 inch 2 lines, (in proportion thereto) fo end of spire 5%3,, 
width =8%:, height =25,, width of mouth 74%.. A very small 
specimen, 43 lines long, has length to end of spire 5%, 
width 52°,, height ;£°,, width of mouth +43,, showing the great 
uniformity of the proportions through all sizes, the very young 
being slightly more globose. 
The greater number of specimens have a very distinctly 
marked, smooth, longitudinal dorsal scar, half the length of the 
shell, interrupting the transverse ridging—one specimen, how- 
ever, having the scar as distinct as usual for a great part of its 
length, has it obliterated at one point by the alternate exten- 
sions of a few ridges from each side a little beyond the middle 
line; and one large specimen has it entirely absent from some 
of the ridges alternating with each other and stretching beyond 
the middle, and others of them joining continuously from side 
to side; when the outer layer of shell bearing the ridges is 
absent, the surface is faintly cancellated by narrow, obtuse, obso- 
lete lines, the spiral or transverse ones about as far apart as the 
ridges of the surface, the longitudinal ones finer, less regular, 
and rather closer. 
This species is so much more globose and has so much fewer 
and more distant ridges than the 7. australis living on the Vic- 
torian shores, that it is not necessary to make any further com- 
parison, It is an exact representative of the Trivia avellana of 
the European Tertiary beds of the same age as those containing 
the present species, but is clearly distinguished by its uniformly 
shorter and more spheroidal form, the nearer identity of length 
and width, the shorter and wider dorsal sulcus almost always 
interrupting the transverse ridges, and the greater curvature of 
the mouth, which is nearly straight in the middle in T. avel- 
lana, but much arched in the present species, in which the 
margin of the outer lip is consequently less inflected ; the sulcus 
is also characteristically shorter than in the European C. avel- 
lana or C. affinis of the Suffolk Coralline Crag and Touraine 
Ann. & Mag. N. Hist. Ser.3. Vol. xx. 30 
