characteristic of Tertiary Beds near Melbourne. 437 



ridges, faintly indented with transverse, broad, scarcely visible 

 marks; the ridges ave 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, joining from each side, 

 effacing the dorsal sulcus, which, when present, varies irregu- 

 larly from half a line to a line in width in 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) to end of spire -jVoj 

 width -ro\} height -fV-Q, width of mouth -riro- A very small 

 specimen, 4^ lines long, has length to end of spire r-^, 

 width -fSjj-%-, height -rxrxj) width of mouth -iVir^ 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 fi'om some 

 of the ridges alternating with each other and stretching beyond 

 the middle, and others of them joiuing 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 T. 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. S^ Mag. N. Hist. Ser.3. Vol.w. 30 



