543 



SOME NEW BRACHIOPODS FROM THE MIDDLE PALAEOZOIC ROCKS 

 OF NEW SOUTH WALES. 



By John Mitchell, latk Principal of the Technical College and School of 



Mines, Newcastle. 



(Plate xxxi.) 



The fossils dealt with in the present paper represent seven genera and as 

 many separate speeies of brachiopods. One genus and four of the species are 

 new. Three of the genera are typically Silurian; one (Merista) is characteristic 

 of Middle Devonian, and the range of the proposed new genus Molongia remains 

 to be ascertained. Two of the species have previously l)een recorded from this 

 State, viz., Betzia salteri Sowerby, by de Koninck from Yarralumla, and Orthis 

 striatula Schloth. by W. S. Dun. From a palaeontological point of view, per- 

 haps the most important of the species under notice is Merista plebe'ia. because 

 it is so typically an index of middle Devonian age in Europe, and in North 

 America; in these countries it has but a limited vertical range For this reason 

 it should be very helpful in correlating the sedimentary rocks in which it occurs, 

 however distant apart they may be. With regard to this fossil it is to be noted 

 that, although its existence was, apparently, only a short one geologically, its 

 distribution was world-wide, and these remarks apply to its a-ssoeiate Orthis 

 striatula Schloth. ; in Australia, just as in Europe, these two fossils are associates, 

 and lielp to confirm the assumption that the rocks in this State, from which they 

 have been collected in association, are approximately of Devonian age. and,^ in 

 that case, they would appear to form an inlier surrounded by rocks of Carbonif- 

 erous age, portions of which have recently been discussed and described (Thess 

 Proceedings, xlv.. 1920, Pt. 2, pp. 285-316). From the same limestone have 

 been gathered a few Sprrifers, one of which is near if not identical with 5. pitt- 

 mani Dun and considered by him to be of Devonian age. The pentamerid, B. 

 m.olongensis, resembles in shape juvenile forms of Barrandella linpuifer var. wil- 

 kinsoni Eth., but in the latter the umbo of the ventral valve is always much more 

 strongly developed and overhanging than it is in the former; and in the latter, 

 too, the length always, at all stages of growth, exceeds the width, while in the 

 former the values of these dimensions are reversed. The Molong fossil occurs 

 with Atrypoittea australis and A. angusta Mitch, and Dun. Etheridge's species 



