E. Wethered — Organisms in Carboniferous Limestone. 533 



structure of the rock generally. In the lowest beds of the series 

 Ostracods have contributed very largely, in some cases little else 

 than the valves of these small Crustaceans make up the limestone. 

 In the upper beds, with the exception of No. 16, they become less 

 numerous, and in some cases are altogether absent. 



Much the same may be said of the Crinoids. Though their re- 

 mains occur throughout the series, they are most numerous in the 

 lowest beds, and in one they are the chief factor, as in Fig. 1. The 

 Polyzoa are most numerous in the Crinoidal bed, but are to be found 

 throughout the Lower Limestone Shales. They are not, however, 

 an important feature in the structure of the rocks with the exception 

 stated. The shells of Bhynchonella pleurodon are very numerous in some 

 beds of black shale, and on weathering taking place, they may be 

 collected in hundreds. The Lower Limestone shales, as with lime- 

 stones generally, represent the floor of a sea in which the organisms 

 lived which we now find in a fossil state. By their death the 

 limestone was formed from the calcareous portions of their structure. 

 The deposition of the strata doubtless extended over a long period 

 of time, during which the conditions were varied, and thus the life 

 varied according as the conditions suited. For this reason we get 

 limestones of different structure and quality, which, of course, was 

 regulated by the organisms which contributed to their formation. 

 The limestone-forming process was at times stayed, during which 

 intervals clays and shales were deposited. The water was probably 

 not deep. This is shown by the amount of sand in the limestone, 

 and also by the great profusion of Ostracods, which class of Crustacea 

 are not abundant in extreme depths of water. 1 



Organisms of the Lower Limestone Shales. 

 Ostracoda. — My specimens have been referred to Professor Eupert 

 Jones, F.E.S., and Mr. J. W. Kirkby, to whom I am indebted for 

 their careful examination. The following is a list of the genera 

 and species which these gentlemen have been able to determine. 

 Probably others exist, but the difficulty of separating them from the 

 matrix, and thus obtaining reliable specimens, prevents a more 

 definite statement being made. 



Kirkbya variabilis, J. & K. 



,, plicata, J. & K. 

 Cytherella extuberata, J. & K. 



Bythocypris sublunata, J. & K. 

 Darwinala Bemiciana (?), Jones. 

 Leperditia OJceni, Munster. 



The above list is especially interesting and important in connection 

 with the Ostracoda recently described 2 by Prof. Jones and Mr. 

 Kirkby from the Gayton boring, Northamptonshire. The material 

 examined yielded six recognizable forms, as follows : — 



Kirkbya variabilis, J. & K. 



,, plicata, J. & K. 

 Bythocypris sublunata, J. & K. 



Comparing the above list with mine, from the Forest of Dean, we 

 find that from the Gayton boring six genera and species were deter- 

 mined, one of which was doubtful. In my list six genera and species 



1 Challenger Report, Zoology, on the Ostracoda, p. 1 . 



2 Geol. Mag. 1886, Dec. III. Vol. III. pp. 248—253. 



Maerocypris Jonesiana (?), K. 

 Cytherella extuberata, J. & K. 

 ,, attcnuata, J. & K. 



