124 ON PERMIAN ENTOMOSTRACA FROM 



cavities that I found the bulk'J of the specimens which form tho 

 subject of these remarks. And it is questionable whether a 

 better matrix for the preservation, and subsequent extraction, of 

 microscopic organisms, than that in which these Entomostraca 

 occurred, can be conceived. It has preserved the specimens 

 which it incloses so perfectly, that they almost rival the produc- 

 cions of recent zoology. In some instances, a brush will remove 

 the investing matrix, without the use of other tools. Occasion- 

 ally the dust is semi-coherent, with nodules or fragments of 

 limestone intermixed ; but in this state the embedded fossils are 

 also easily extracted, without much assistance from palseontolo- 

 gical instruments. Some of the finest specimens ever taken from 

 the Permian beds in Durham have been got from these cavities, 

 and also some of the rarest species. An analytical examination 

 of the contents of some show very curious results. For instance, 

 in one, I found about one hundred and fifty perfect and imperfect 

 spines of Cidaris KeyserUngi, Kii^g? and with them but one or 

 two fragments of the plates of that species ; in another I got 

 more than one hundred dorsal valves of young individuals of 

 Strophalosia Goldfussi, MUnst., which w^ere accompanied by only 

 fifteen ventral valves. Of course, in both cases, other species 

 were associated, but the remains of those mentioned were the 

 most prevalent, and, by their abundance, and peculiar mode of 

 occurrence, formed the characteristic feature of the contents of 

 each cavity. Such facts are very puzzling, and would almost 

 seem indicative of a drifting of specimens prior to fossilization — 

 an idea which is scarcely tenable, when the general evidence of 

 the whole fauna is considered. 



The majority of the specimens of Entomostraca which were 

 found belong to species of Bairdia, with scarce, but good, ex- 

 amples of a Bei/richia-like species, previously noticed in the upper 

 limestone by Jones, and provisionally referred by him at that 

 time to the genus Dithyrocaris of Scouler,* but now recognised as 

 a new genus under the name of KirHhya (see further on). The 

 Bairdioi generally occurred with united valves, though single 

 valves were not nncommon. The specimens of the latter species 



* " Mon. Perm. Foss.," p. fi4. 



