On the Limits and C^assijication of the Ganoids. 329 



epitome of a coal-scam : its roots represent the Stigmaria- 

 underclay ; its bark the compact coal ; its woody axis the 

 mineral charcoal ; its fallen leaves (and fruits), with remains 

 of herbaceous plants growing in its shade, mixed with a little 

 earthy matter, the layers of coarse coal. The condition of the 

 durable outer bark of erect trees concurs with the chemical 

 theory of coal, in showing the especial suitableness of this 

 kind of tissue for the production of the purer compact coals. 

 It is also probable that the comparative impermeability of the 

 bark to mineral infiltration is of importance in this respect, 

 enabling this material to remain unaffected by causes which 

 have tilled those layers consisting of herbaceous materials and 

 decayed wood with pyrites and other mineral substances." 



XLT. — On the Limits and Classification of the Ganoids. 

 By Dr. C. LiJTKEN*. 



In my memoir on the limits and classification of the Ganoidei 

 (Om Ganoidernes Begrajndsning og Indcling, Copenhagen, 

 1869) my only object was to summarize and expound the re- 

 sults at which science has arrived with regard to the impor- 

 tant question above indicated ; and its importance, whatever 

 this may be, is due solely to the necessarily restricted number 

 of those who have had the time, patience, and leisure to be- 

 come thoroughly acquainted with these results by their own 

 investigations. Certainly the history of palaichthyology 

 shows very plainly that hitherto this question has not been 

 perfectly clear, in part because several of the most eminent 

 authors have, unfortunately, been unable to obtain an exact 

 knowledge of the works of their predecessors. Hence, at least 

 in part, arises the uncertainty as to the definition and limits of 

 the Ganoidei, the rank which they should occupy in the zoo- 

 logical scale, the mode of subdividing them, &c. Have we 

 not seen Andreas Wagner, whose memoirs on the fishes of the 

 Lithograjihic Limestone constitute one of the greatest triumphs 

 of palajichthyology, contenting himself with a definition ap- 

 plicable only to a particular formation ? and Rodolph Kner, 

 the learned describer of the fishes of ancient and recent times, 

 expressing the opinion that, at bottom, there are no Ganoids 

 at all, and that the forms united under this name are nothing 

 but the prototypes of the different existing ichthyological 

 families, having nothing in common but a character of anti- 

 quity? England and southern Germany have been the })rin- 



* Trnnslated by W. S. Dallas, F.L.S., from tlio ' Bibliotheqiie Uiiiver- 

 selle,' March lo, 1^71, Arch. d.>.s Sci. pp. 283 i'9(5. 



