836 APPENDIX. 



The Vertical Range of the Mollusca. — Of the twenty species of 

 lamellibranchs recorded above, three are very common and range 

 throughout more than 2,500 feet of strata, they are: — 



Carbonicola aquilina. 



„ acuta. 

 Naiadites modiolaris. 



The range of the following three species is also very wide : — 



Carbonicola similis. 

 „ turgida. 



Anthracomya modiolaris. 



C. similis occurs in the roof of the Kilburn Coal and also in the roof 

 of the Top Hard Coal some 1,300 feet above; but, in spite of repeated 

 search, this shell has not yet been found in the intervening measures. 



Anthracomya Phillipsii appears to be restricted to the highest 

 measures above the Top Hard Coal. The following four species have, 

 up to the present, been found only in the middle portion of the sequence 

 between the Mainbright Coal and the Deep Hard Coal : — - 



Carbonicola obtuxa. 



,,' subconstricta. 



„ ovalis. 

 Anth racomya Williamsoni. 



The lowest measures between the Deep Hard Coal and the base of 

 the coal-measures are characterised by the presence of the following 

 four species : — 



Carbonicola robusta. 



„ nucularis. 



„ acuta, var. rhomboidalis. 

 Anthracomya laevis, var. scotica. 



In addition to the species of mollusca recorded above, it has been 

 observed that several intermediate varieties, showing gradational forms 

 between two or more species, are by no means rare. 



