81 



waters. The time, however, may be distant, as the coast is little settled 

 upon, except in the neighbourhood of Swan River. There is the more 

 probability of ita being found seeing that the genus is thoroughly Aus- 

 tralian as a recent form, and also from the fact that the mollusc itself is 

 migratory in its habits. Like many other bivalve molluscs, Trigorda is 

 able to make considerable leaps by means of its powerful wedge-shaped 

 foot; and Woodward in his " Manual" mentions an instance in which 

 a specimen, placed by Mr. Stutchbury on the gunwale of his boat, leaped 

 overboard, clearing a ledge four inches in height. Neither is there any 

 record of the existence of Trigonia in the seas of New Zealand ; but 

 perchance time may add it to the already extensive fauna of the shores 

 of that country also. The recent T. pectinata of the adjacent coast of 

 New South Wales is found as a fossil in the upper miocene rocks of 

 New Zealand. 



I will now briefly refer to Trigonia as a fossil in Australia, and for 

 numerous references and notes, and very complete information, mostly 

 obtained by his own personal observation, I am indebted to Professor 

 Tate. 



Seven fossil species are known — two from Jurassic, one from cre- 

 taceous, and four from tertiary strata. In point of age, the first to be 

 mentioned are the two Jurassic species, as in them we have contem- 

 poraneous representatives of the genus Trigonia when it first made its 

 appearance in the ever-developing scheme of Creation. 



1. T. Moorei, Lycett.. Western Australia, allied to T. costata of 



the European Oolite ; and 



2. T. lineata, Moore, Wollumbilla, Queensland. Both these spe- 



cies are described in the Jour. Geol. Soc, Vol. xxvi., 1870. 

 Next in geological sequence comes the cretaceous form. 



3. T. nasuta, Etheridge, from Maryborough, Queensland. It is 



allied to T. alceformis, and belongs to a type not known in 



the Jurassic rocks. 

 We now come to the Tertiary species, the forms, as a consequence, 

 having the closest affinity to the recent species referred to in the earlier 

 part of the paper. 



4. T. semiundtjxata, McCoy. Prodromus of the Palseontology of 



Victoria Decade, II. t. 19, f. 1—2, pi. 21. 

 Professor McCoy says this shell is " easily distinguished from any 

 known recent or tertiary species by the rippled appearance produced by 

 the undulated concentric ridging of the anterior two-thirds of the valves. 



