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- 



althoiigh 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 diiFerent 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 1 think to make a 

 change now without producing more confusion than the change 

 would be worth. 



I have the honour to remain, Gentlemen, 

 lUgnqi?!! Your most obedient servant, 



Frederick M'Coy. 



XVII. — Contributions to the Botany of South America. 

 By John Mters, 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 Witheringia picta, as figured by Martins (Nov. Gen. 

 tab. 227), 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. 



