Mr. J. Miers on the genus Witheringia, 141 



case from his ' Odontography/ where he had himself inadver- 

 tently called it " enamel " in describing a fossil tooth [Peta- 

 lodus), although in other places he had described it as it 

 is. Prof. Agassiz I believe in all his descriptive characters 

 has called it "enamel," and so have most writers. The case 

 therefore stands now as before, namely, that a peculiar modifi- 

 cation of tissue exists in certain fish-teeth, very different from 

 " enamel," yet confounded with it by many writers, frequently 

 called " enamel " in the technical descriptions, and for which no 

 other term had hitherto been proposed ; my object now is to state, 

 that in proposing the term " ganoine " for the sake of brevity and 

 accuracy in the descriptions of the fossils I was engaged on, I by 

 no means intended to impute ignorance of its structural peculi- 

 arities to any preceding writer. If I had been aware that Prof. 

 Owen had used the word in question orally at his lectures for the 

 polished part of ganoid scales, and that he would have preferred 

 " vitro-dentine " for the dental tissue, I should of course have 

 used it also ; but as those terms have not been so published, while 

 mine is already current, it is scarcely possible I think to make a 

 change now without producing more confusion than the change 

 would be worth. 



I have the honour to remain. Gentlemen, 



Your most obedient servant, 



Frederick M'Coy. 



XVII. — Contributions to the Botany of South America. 

 By John Miers, Esq., F.R.S., F.L.S. 



Witheringia. 



The following observations will I hope serve to throw some 

 light upon this hitherto obscure genus. It always appeared to 

 me that the M'itheringia picta, as figui'cd by Martins (Nov. Gen- 

 tab. 327), must either form the type of a very distinct group, or 

 be considered as a very good illustration of that genus, for which 

 reason I refrained from publishing what I had long ago observed 

 on the subject, until I could satisfy myself of the absolute cha- 

 racter obscurely indicated by L'Heritier, in regard to his typical 

 species W. solanacea (Sert. Angl. 33. tab. 1). Under this un- 

 certainty (in a note, Lond. Journ. Bot. iv. 353) I alluded to the 

 unsuccessful search I had everywhere made for some specimen, or 

 better details, of the plant in question, so as to be able to com- 

 prehend the limits and features of the generic character of 

 Witheringia, and I expressed my regret that the original type no 

 longer existed in L'Heritier's herbarium in the British Museum, 

 as that would at once have cleared up this ambiguity. Dr. 



