lo-l ON I'ERMIAX ENTOMOSTRACA FROM 



afterwards Dr. Ricliter figured and described another, somewhat 

 differing from the foregoing, under the same appellation, from the 

 dark-grey limestone of the Lower Zechstein of the Roth Berg, 

 near Saalfield, and recognised its probable affinity to the so-called 

 Dithyrocaris Permiana. 



The numerous fine specimens, however, obtained by Mr. Kirk- 

 by from the Magnesian limestone of Tunstall Hill enabled him, 

 last year, to draw up an exact description of these interesting 

 Entomostraca ; but, thinking that I might have means for a 

 wider comparison than he possessed, and knowing that I had 

 already interested myself in the subject, he most courteously and 

 considerately left to me the determination of the generic alli- 

 ances ; and liberally confided to me all his materials for exami- 

 nation. The result has been that, after a careful comparison of 

 Silurian, Carboniferous, and Permian species of near alliances, I 

 believe that we have, in these peculiar Permian forms, and in a 

 related species from the Lower Carboniferous rocks of Scotland, a 

 distinct generic type not far removed from Beyricliia. For this 

 genus I propose the name oiKirkhya ; for without Mr. Kirkby's in- 

 dustrious researches and acute observation, we should still have 

 wanted the abundant and illustrative materials which we now 

 possess for the natural history of this Permian species. 



I had recognised in the figures and descriptions given by Eeuss 

 and Richter of their Cythere Eoessleri an affinity to my so-called 

 Dithyrocaris Permiana and D.glypta; and, in the autumn of 1857> 

 Dr. Richter favoured me, at Saalfeld, with two specimens of the 

 species which he had described as Cythere Eoessleri (Reuss); but 

 the finely -sculptured surface of the German specimens offered 

 so strong a contrast to the bareness of the valves from Byers' 

 Quarry, that I gave up the hope of finding more than a consangui- 

 nity between these peculiar English and German Entomostraca ; 

 and I trusted to be able some day to point out that they were 

 neither Dithyrocaris^ Cei^atiocaris, nor Cythere. 



The carapace-valves from Saalfeld had presented to me not 

 only a finely reticulated surface (well figured by Richter), but also 

 a small subcentral sunken oval spot, around the smooth edge of 

 which the meshes of tlie superficial net-work had a more or less 

 distinct concentric arrangement for a little space. Of this fea- 



