W. S. Hudleston — On the Torkshire Oolites. 257 



require some latitude in the determination of these points. Certain 

 demoid types are, it seems to me, the same in the Dogger and in the 

 Corallian Rocks, such as Cerithium muricatum, and probably species 

 of Littorina and Deljphinula, which are certainly difficult to distin- 

 guish from well-known Corallian forms. On the other hand, the 

 abundant Chemnitzia Uneata-procera of the Dogger has its representa- 

 tive species on the higher horizon in Chemnitzia Heddingtonensis, 

 And so it is with most of the Corallian species : they are representa- 

 tive rather than identical, yet in many cases possessed of a strong 

 family likeness to their predecessors of the Dogger. The following 

 Corallian genera have not yet been enumerated in the Dogger, viz. 

 Purpiiroiden, Pseudomelania, and Cylindrites. 



For purposes of comparison we must treat the Millepore Rock and 

 Scarborough i/imestone as one zone, owing to the difficulty of 

 sepai'ating the specimens in those cases where the nature of the 

 matrix cannot always be relied upon to assist in the discrimination. 

 Together they contain about half as many species as ai'e yielded by 

 the Dogger : the most abundant forms are decidedly those of the 

 Dogger fauna, especially in the Millepore Rock, as might be expected. 

 About one-third of the species in the Scarborough Limestone, or third 

 zone, passes up into the Cornbrash, where, however, the prevailing 

 species are very different. Somewhat less than a third of the Corn- 

 brash species passes up into the Kelloway Rock. Hence the Cornbrash 

 occupies a somewhat isolated position as regards its Gasteropoda. 

 The few species which occur in the " Oxford Clay " are, with one 

 remarkable exception, forms which have been noted in the Kelloway 

 Rock, and almost the same may be said of the few species known 

 from the Lower Calcareous Grit — at least these latter are, for the 

 most part, no more than varieties. 



As before observed, the Gasteropod fauna of the Yorkshire Oolites 

 had now sunk to an extremely low ebb, previous to that wonderful 

 revival of which the Corallian Rocks have afforded such excellent 

 proofs. 



End of Memoir No. 2. 



ERRATA. 



Memoir No. 1. 



Geol. Mag. 1881. 

 p. 122, line 11, for 'had' read 'have.' 

 p. 127, line 4, for ' 1870 ' read ' 1810.' 

 p; 127, below line 16, insert Actceon retusus, Phillips, G. Y. pi. iv. 



Memoir No. 2. 



Geol. Mag. 1882. 

 p. 193, line 18, for Pictte read Pietti. 

 p. ib. line 20, for ' Superior ' read ' Inferior.' 

 p. 250, line 17, for ' Monti.' read 'Montr.' 



Geol. Mag. 1884. 

 p. 200, line 11, for CeritU<B read Cerithia. 

 p. 245, line 3 from bottom, for armata read armigera. 

 p. 201, line 4 from bottom, dele ,. 



,, line 5 from bottom, for turrited read tivisted. 



DECADE III. — VOL. II. — NO. VI. " 17 



