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On A Variety of TRIGONIA LAMARCKII.

by Rev. J. E. TENISON-WOODS, F.G.S.

I beg to call attention to an interesting variety of Trigonia Lamarckii, which I designate thus:-

Var. A, Reticulata. Testa tenui, parva, costis acutis, nodulis subspinosis, tota testa peculiariter reticulata.

This shell was dredged outside Port Jackson Heads by Mr. John Brazier, at a depth of 45 fathoms. The shell is small and thin, and the ribs are sharp, while the nodules are almost spinous. The whole surface is very finely reticulated or perhaps it would be more correct to say shagreened.

The fact of this variety having sharp ribs is of importance, as a fossil form is found in our Australian Cainozoic rocks, whose main point of distinction from the living T. Lamarckii is the possession of acute ribs and spinous nodules. This is McCoy's T. acuticostata. The present variety cannot be said to be a young shell, because young shells do not present any such peculiarities as may be seen from the specimens exhibited.

We have six described species of Trigonia in Australia, viz. - ­T. Strangeii, T. Lamarckii, T. margaritacea, T. pectinata. T. uniophora, and T. Jukesii. Probably there are only four distinct species, as T. Lamarckii and T. pectinata are the same, and T. Jukesii, Adams is a synonym for T. uniophora of Gray. See Voy. of H. M. S. "Fly."

There are two or three fossil species in our Australian Tertiary deposits, viz. - T. semiundulata, McCoy, T. acuticostata, McCoy, and T. Howitti, McCoy.