DESCRIPTION OF SPECIMENS. 



In tie descriptive part of this Catalogue the species are grouped, 

 as far as possible, in accordance with their natural affinities. Some 

 of the genera are discussed at length, but in the majority of cases 

 reference must be made to the two volumes on the Weal4^E^a ' 

 for an account of the history and application of generic nmias, as 

 also for definitions of Families and Classes. Several of the specimens 

 are from the collection of William Bean, and these usually bear 

 a label with his determination. Bean's names are often quoted in 

 the description of the specimens as occasionally throwing light 

 on the current use in his day of various specific names ; but, on 

 the other hand, it is necessary to exercise considerable caution in 

 attaching importance to the determinations of this enthusiastic 

 collector. The localities are, in many cases, too vague to serve as 

 guides to the exact horizon from which the plants were obtained ; 

 we frequently find nothing more than "near Scarborough," "near 

 Whitby," " Scarborough," etc., indicating that, as a rule, the 

 necessity of giving accurate information as to the position of the 

 beds had not been realized. 



In several instances the difficulty of determination has been 

 considerable, owing to the constantly recurring question as to the 

 advisability of uniting a series of specimens under one specific 

 name or of emphasizing the existence of slight dijfferences by the 

 use of distinct names. It frequently happens that the examination 

 of the material in a single collection leads to the view that certain 

 forms are specifically distinct ; but the abundance of specimens in 

 several museums often supplies transitional forms which render 



1 Seward (94 >) (95). 



