77 



AUSTRALIAN TRIGONIAS AND THEIR DISTRIBUTION. 



By W. T. Bednall. — (Communicated by Prof. Tate). 



(Read June 18th, 1878). 



It has occurred to me that a few remarks introducing to the notice 

 of this Society a form of life peculiar in recent times to the Australian 

 seas might prove interesting, especially as it is connected with a branch 

 of Natural History, which although affording an extensive field for observa- 

 tion and research in this colony, is seldom taken up by members of this 

 body, with perhaps the exception of Professor Tate, namely, Conchology. 



I have the more particularly chosen the theme from the fact that it 

 has been my very good fortune to be the first to discover the most western 

 limit, at least so far as at present known, of the genus both on the coast 

 of North Australia and on the southern shores of the continent. 



The genus Trigonia was founded by Bruguiere, a French naturalist 

 of the last century, to represent a group of bivalve shells of a triangular 

 or three-cornered shape (as the name implies), peculiar to the secondary 

 rocks of Europe, and at that time known only as fossils. They first made 

 their appearance in the Lias, whence they extended through the Lower 

 and Upper Oolite to the Cretaceous series, where they disappeared ; the 

 Tertiary formations in no part of the world but this, having produced any 

 individuals whatever. The genus numbers but few living species, but is 

 particularly rich in fossil representatives. Upwards of 100 species were 

 known from the oolitic and cretaceous rocks of Europe, the United 

 States, Chili, the Cape, and Southern India, more than twenty years ago, 

 and now the number must be nearly double that. Australia is, however, 

 the home of these remarkable shells in a living state, and thus adds 

 another instance in which this great southern island-continent is the 

 habitat of forms of life which in other parts of the globe are only found, 

 to use Dr. Mantell's appropriate term, as " Medals of Creation." 



