320 Mr. J. W. Kirkby on Permian Entomostraca 



In the calcareous dust which contained the Entomostraca were 

 also a number of specimens of a curious Foraminifer, apparently a 

 species of Miliolina^. Several species of Mollusca also occurred, 

 as Productus horridus, Spiriferina multiplicata, Camarophoria 

 Schlutheimi, Crania Kirkbyi, Monoiis speluncaria, Pleurotomaria 

 nodulosa, &c. The convex valve of the conchifer appears to 

 have been a popular place of resort with the Bairdi(S. Out of 

 one I procured some dozens of individuals. 



It is also worthy of remark, that in close vicinity to the Ento- 

 mostraca there occurred some of the rarest Permian fossils, and 

 others that were previously unknown ; also an abundance of 

 specimens belonging to species hitherto rare in the limestone of 

 Tunstall : so that the evidence deducible from the fossils asso- 

 ciated with the Entomostraca, and from those in their immediate 

 neighbourhood, may imply some peculiarity of conditions per- 

 taining to this particular area during the deposition of the fos- 

 siliferous limestone. 



During the Permian period, the prevailing forms of Ento- 

 mostraca seem to have belonged to two groups, — to Bairdia, and 

 to an undetermined genus, of which Dithyrocaris ? Permiana, 

 J ones t, and Cy there 1 Roessleri, UeussJ, are members. Bairdia 

 is the most characteristic of the Permians of Western Europe ; 

 in fact, it is unknown as yet in the Permian rocks of Russia. 

 In Germany it is represented by several species, and by a greater 

 number in Durham ; a single species occurs in the Yorkshire 

 Permians ; and Prof. King has observed another (?) in the Pei'mian 

 deposit of TuUyconnel. In the fossiliferous limestone of Durham 

 the Entomostraca almost exclusively consist of species of this 

 genus, from which it may be inferred that the conditions prevail- 

 ing during the accumulation of that deposit were highly suitable 

 for their development. Bairdia seems to represent the Mesozoic 

 element in this section of the Permian fauna, it being more pro- 

 perly a Mesozoic group, although it is first met with in Palaeozoic 

 beds. As a connecting link with the older rocks, the generic form 

 typified by the above species, D. Permiana and C. Roessleri, may 

 be noticed as a representative of its more ancient prototypes, the 

 Beyrichia and Leperditia of the early Palseozoics. This form 

 predominates in Russia; three species occur there §. Another is 

 found in Germany, and two in Durham. According to our pre- 

 sent knowledge, these species are all that belong to this genus, 

 no similar forms having, as yet, been found in other rocks ; con- 



«*• 



* It is the same fossil as Geinitz's Serpula pusilla and the Spirillina 

 pusilla of Jones. 



t Mon. Perm. Foss. p. 66. 



X Jahres. Wetter. Gesell. 1851-1853, p. 70. 



§ Reise dm-ch die Timdren der Samojeden, 1854, p. 112. 



