Tertiari/.] PALEONTOLOGY OF VICTORIA. IMollusca. 



very small specimen 4^ lines long- has leng'tli to end of spire, -i%% ; width, j^g%; 

 heig'ht, -f^"^; width of mouth, -j/a; 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 distmctly marked 

 smooth longitudinal dorsal scar half the length of the shell inter- 

 rupting the transverse ridging ; one specimen, however, having the 

 scar as distinct as usual in great part of its length has it obliterated 

 at one point by the alternate extensions of a few ridges from eacli 

 side a little beyond the midline ; 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 joining con- 

 tinuously from side to side. When the outer layer of shell bearing 

 the ridges is absent the surface is faintly cancellated by narrow 

 obtuse obsolete 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 Trivia Au.stralis living on the 

 Victorian shores that it is not necessary to make any further 

 comparison. It is an exact representative of the Trivia avellnna 

 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 inter- 

 rupting the transverse ridges, and the greater curvature of the 

 mouth, which is nearly straight in the middle of T. avellana, but 

 much arched in the present species, in which the margin of the 

 outer lip is consequently less inflected ; the sulcus is also charac- 

 teristically shorter than in the European C. avellana, or C. affinis of 

 the SuflTolk Coralline Crag, and Tourain beds, with which latter it 

 agrees better in its usually naked sulcus, but the ends of the ridges 

 are never dilated, and in addition to the same differences of the 

 more arched mouth and less inflected outer lip of the Australian 

 species, the shell in it is larger, thinner, and the ridges more 

 elevated, thinner, and farther apart. 



Very common in the l)lue Oligocene Tertiary clays and limestone 

 between Mount Eliza and Mount Martha, in the Bay ; very rare but 



C 37 ] 



