246 



F. CHAPMAN. 



Parish of Taemas, Co. of Cowley. In beds containing 

 Chonetes culleni, Dun. Presented by Mr. A. J. Shearsby, 



F.R.M.S. 



Note on Ostracodal Limestone from the Middle Devonian 

 of Cavan, Yass. 



Accompanying the foregoing specimen of Primitia there 

 is a microscopic slide prepared by Mr. Shearsby, of a frag- 

 ment of an Orthoeeras shell from the Devonian Limestone 

 of Oavan. This thin slice is seen to be crowded with the 

 separate valves and carapaces of at least three species and 

 probably two genera of Ostracoda. The commonest forms 

 are clearly referable to Primitia, whilst occasionally there 

 is a rather peculiarly shaped form with a long spinous pro- 

 cess, reminding one of Mchmina. The affinities of this 

 latter type are at present conjectural, as there are no very 

 definite or complete outlines of the carapace in the slice 

 examined. Of the Primitice, one form, the more common, 

 is moderately short-ovoid, and resembling generally the P. 

 cuneus before mentioned, of the Middle Devonian of Buchan, 

 Victoria. The other species is long-ovate, anteriorly 

 acuminate in edge view, with an antero-median sulcus. 



The general characters of the limestone are, a sub- 

 crystalline rock, very compact, crowded with ostracodal 

 remains. The matrix or cement is a moderately fine calcitic 

 mud, almost entirely re-crystallised, and completely filling 

 up all the interspaces between the organic remains. Besides 

 the ostracoda there are small ossicles of crinoidal origin. 

 The ostracodal valves show the original typical micro- 

 fibrous structure and characteristic dark brown colour as 

 compared with the pelecypod shells; whilst in many of the 

 interiors of the still perfect carapaces, remains of the 

 original animal-organism are seen in the patches of carbon 

 particles still enclosed within the valves. 



