IW. W. C Williamson. Correction of an [Apr. 26, 



roust I be understood to say that all shying IB due to defective eye- 

 sight ; further, it is possible for defective vision to be present 

 without shying occurring, notably in Case 23 and several others. 



Berlin considered the majority of horses to be hypermetropic ; I 

 have only met with one case of very low hypennetropia out of 100 



eyes. 



Conclusion. 



1. The chief visual defect in horses is myopia with or without 

 astigmatism. 



2. The amount of error is not great. 



VI. "Correction of an Error of Observation in Part XIX of the 

 Author's Memoirs on the Organisation of the Fossil Plants 

 of the Coal Measures." By W. C. WILLIAMSON, LL.D., 

 F.R.S. Received March 28, 1894. 



During the past two or three years we have acquired a much more 

 accurate knowledge than we previously possessed of the structure of 

 the leaves of the Lepidodendroid plants of the Coal Measures ; and 

 my last memoir, published in vol. 184 (1893) of the Philosophical 

 Transactions, contains some new and not unimportant details on this 

 subject. These facts were obtained from some finely preserved 

 specimens of Lepidodendron Harcourti and of a Lepidophloios 

 recently added to my cabinet. 



But the value of these observations was seriously vitiated by an 

 apparently small but very fundamental error into which I had fallen, 

 an error which cannot be left uncorrected without misleading some 

 of the palaeontologists who honour me by consulting my writings on 

 these subjects. 



The students of fossil botany have long distinguished the leaves of 

 the Lepidodendron from those of the Genus Lepidophloios by the 

 shape of the leaf-scar left on the pulvinus or leaf-cushion on the fall 

 of the deciduous leaf. These scars are always more or less quadri- 

 lateral in form, two of their angles following in opposite directions 

 the long axis of the parent stem or branch, the other two pointing 

 transversely across that axis. In Lepidodendroid leaves there is 

 little difference in the lengths of these pairs of decussating angles, 

 but in Lepidophloios the two transverse ones are much more pro- 

 longed than the vertical ones are, making the transverse diameter of 

 the leaf-scar greatly exceed that in the opposite direction. 



Whilst attached to the stem or branch of a Lepidodendron these 

 leaves always point upwards towards its apex ; and when I wrote the 

 memoir referred to above, I had no reason for supposing that this 

 was not also the case with the foliage of Lepidophloios, and my two 





