In No. VI. of the “Quarterly Journal of Science” I gave a brief account of the Trigonia semiundulata, M'Coy, MS., which has been found in certain Tertiary strata in the Colonies of Victoria and South Austraila, and which had been named, but not described, by Professor M'Coy. This species differs altogether from the recent forms, and approaches very closely in its essential characters to the members of the group “costata”, characteristic of the Oolites. It was therefore remarked, in the communication referred to, that its occurrence in Tertiary strata in Australia added another link to the chain of evidence which connects the recent fauna of that region with the Oolitic fauna of Europe. But doubt may be expressed as to the exact value to be assigned to this similarity in facies between two faunæ so widely separated in time; and it is a fair question whether the discovery of this Trigonia does not diminish, rather than add to the apparent peculiarity of the existing Australian fauna.