318 Mr. J. W. Kirkby on Permian Entomostraca 



These, I believe, comprise all the Permian Entomostraca which 

 have been noticed up to the present time. 



The following remarks refer to the Entomostraca belonging 

 to the fossiliferous or shell-limestone of the Permian System of 

 Durham. This deposit lies below the beds whence the species 

 described by Mr. Jones were procured. It occupies a central 

 position in the calcareous beds of the system, being situated 

 between the lower or compact limestone and the various beds of 

 the upper members. Consequently the Entomostraca of this 

 deposit belong to a period antecedent to that of the previously 

 described Durham species. In Britain they have not yet been 

 observed in Permian rocks of an earlier date ; but in Germany 

 they occur, as before stated, in the Lower Zechstein, which is 

 equivalent to our compact limestone. This proves their exist- 

 ence during the deposition of the first calcareous beds of the 

 Permian series of Western Europe, and gives them a place in 

 the fauna of each of the three members into which this series of 

 rocks has been divided. Although they appear to have existed 

 throughout the period during which the whole of the calcareous 

 beds were accumulated, it is evident that their distribution was 

 not at all general : otherwise their absence in the compact lime- 

 stone of Durham, in the Zechstein Dolomit, Stinkstein, and 

 Rauchwacke of Germany, would not have been observed; nor 

 would they have been so rare, in respect to localities, in those 

 members in which they do occur. In the upper beds of Durham 

 they are only found in one locality (Byers' Quarry)*. In the 

 fossiliferous limestone they are only found at Tun stall, with the 

 exception of a stray example occasionally met with at Humbleton 

 Hill. At Tunstall Hill they are not generally dispersed through- 

 out the locality ; it is only at one particular spot that they occur 

 in any abundance, — or rather, in which they have occurred, for 

 the spot seems already exhausted. In this place they were very 

 plentiful, some hundreds of specimens having been obtained 

 from a few cubic feet of matrix. 



In the limestone of Tunstall Hill, there occur cavities which 

 are filled with brown or yellow calcareous dust. Sometimes they 

 contain yellow or brown dust, and nothing more; at others, 

 groups of very finely preserved fossils are mixed with the dust. 

 These cavities have already been noticed by Mr. Howse, who 

 long ago detected the richness of their contents f. It was in one 

 of these that I found the various forms of Entomostraca to be 

 noticed in this paper. It is questionable whether a better matrix 



* See Jones in Mon. Perm. Foss. p. 60. 



t Catalogue of Fossils of Perm. Syst. of Northumb. and Durham, p. 9. 

 Mr. Howse has also observed similar cavities in the fossiliferous limestone 

 of Silksworth. 



