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I. — INTRODUCTION. 
Three species, referable to the genus Try plasma, Lonsdale, as I understand 
it, have, so far, been described from Australian material, all from Upper 
Silurian strata. The first, T. Lonsdalei, milii, may be regarded as the 
Australian type, and represents the fasciculate forms ; the second, T. 
wellingtonensis, milii, represents the turbinate-conical species, and the third, 
T. (?) Murrayi, milii, again appertains, more or less, to the fasciculate division. 
The first two occur in New South Wales and the third in Victoria. 
At the inception of my study of this remarkable genus, I had no 
conception of the wealth of material available, nor of the protean character of 
the species comprising it. Tryplasma is one of the most important genera 
met with in our Silurian rocks, several of its species indicating well defined 
stratigrapliical horizons, just as the late Dr. G. Lindstrom has noted in the case 
of the occurrence of his T. ( Pholidophyllum ) tub ul at am in the Gotland Lime- 
stone. The occurrence of Tryplasma in Australia, so far as its stratigrapliical 
distribution is at present known, always indicates rocks of Upper Silurian 
age. At any rate only one doubtful instance to the contrary is known, 
although in Germany, where it has been recognised under the names of 
Calophyllum and Coelophyllum, it passes into the Stringocephalus Limestone 
of the Middle Devonian. The importance of Tryplasma as a stratigrapliical 
factor will be readily understood when its occurrence at no less than forty- 
six different localities is pointed out. It is also a world-wide form, the 
geographical distribution having been indicated by Lindstrom under the name 
of Pholidophyllum. 
