20 



landicus, var WilJcinsoni, has been accordingly forwarded to 

 Sydney for publication. So far as I am aware, the above 

 extracts give an outline of all that has been written on the 

 subject of fossil Unionidce in Australasia, although I should 

 imagine, from the widespread nature of certain Post-Tertiary 

 deposits over the continent of Eastern Australia, containing 

 the remains of Di2)rotodon, gigantic kangaroos, and other 

 extinct mammals, associated with fluviatile and brackish 

 water mollusca, that shells of the Unionidce will likewise be 

 met with. 



To return to the JJnios from the Tamar Eiver. Specimens 

 first came under my notice in a collection of Tasmanian 

 fossils, presented to the British Museum by Dr. Milligan, 

 and being, so far as I could ascertain, not directly i^oticed, 

 I wrote on the subject to my friend Mr. E. M. Johnston, 

 who has kindly supplied me with the following facts: — % 

 " Specimens of the TJnio sp. of the ' Launceston Tertiary 



Basin,' which has not yet been described are 



now for the most part in a state of ' brown hematii.e,' matrix 

 a ferruginous clay, associated with leaves described by me in 



my first paper on the Launceston Tertiary Basin 



I could never get a glimpse of the hinge teeth. It, perhaps, 

 may be identical with your V. WilJcinsoni, which I have 

 never seen." 



Dr. Milligan's specimens quite bear out Mr. Johnston's 

 •description of their conversion into brown hematite, and so 

 far has this alteration proceeded, that it is with difficulty the 

 more detailed characters of the species can be distinguished. 

 Amongst Dr. Milligan's specimens there are undoubtedly 

 two distinct forms, one having the outward aspect of a JJnio 

 proper, the other that of an A^iodon, the latter being repre- 

 sented by the least number of examples, but all possessing 

 the same ferruginous appearance, 



The following is a description of the species : — 

 Genus Unio, Kitzius, 1788. 



Unio Johnstoni, Sjp. non. (Fig. 1 and 2), Sp. char. Shell 

 transversely elongated, accuminated towards the posterior ; 

 anterior end convex and very gibbous ; posterior end 

 bluntly pointed, and gradually accuminated from the anterior 

 •end ; anterior margin obliquely rounded downwards; posterior 

 margin narrow and rounded ; hinge line straight, gradually 

 descending from the umbones towards the posterior end ; 

 ventral margin gently rounded or convex, entire, no sinu- 

 ation ; flanks of the shell most convex at a point on the 

 anterior end midway between the beaks and the ventral 

 margin, whence the sides rapidly decline to the latter, 



X In a letter dated "Launceston, 9th June, 1879." 



