Vol. XXviii.] PALEONTOLOGY OF LANCASHIRE COAL MEASURES. 643 



Ostracods occur in the measures of each district. 



The moUusca occur on the whole but sporadically until 

 the higher seams are reached. This is noticeable in each 

 district. 



List of Fossils Found in the Lower and Middle 

 Coal Measures. 



The accompanying list includes all the genera and species 

 from the Lower and Middle Coal Measures which are known 

 to the writer. 



It will be seen that the list comprises about 75 genera and 

 137 species. Of these 42 genera and 73 species occur in the 

 Lower series, and 60 genera and 106 species in the Middle, 

 whilst no less than 28 genera and 36 species are common to 

 the two, or in other words, 28 genera and 36 species pass up 

 from the Lower into the Middle Coal Measures. As stated else- 

 where, the fish fauna dominate the Middle series, and inasmuch 

 as this development is shown in the roof of the Arley Mine, 

 the lowest seam and the base of the series, it follows that 

 the latter constitutes, not only an account of its constant 

 character over the whole coalfield, but also on account of its 

 palaeontological features, a good line of demarcation between 

 the Lower and Middle Coal Measures. The question of 

 where the Upper limit of the Middle Measures must be 

 drawn cannot be dealt with until we are able to tabulate the 

 fossils of the Upper Series. 



At present, the Upper limit is recognised as the Worsley 

 four-feet, but a tendency has been shown latterly by 

 palaeobotanists to split up the Upper series, putting the 

 lower portion with the Middle Measures, and adding the 

 upper portion to the Permian. 



