The Fossil Plants of the Coal Measures. 57 



most experienced observers. Under these circumstances 

 I strongly object to the undue multiplication of generic and 

 other names that are so common amongst us. Where we 

 find considerable groups, the individuals composing which 

 have certain very definite features existing throughout the 

 entire group, as is the case, for instance, with that of the 

 Zygopterids, it seems to me useful to give them a common 

 name. But the cases are numerous in which this cannot 

 be done. In such types each example would require a 

 name of its own. This necessity would arise, partly from 

 the imperfection of the fragments with which we have 

 to deal, but also, in part, from the absence, in many 

 such instances, of sufficiently individualised features to 

 make their differences easy to define. In such cases as 

 Lyginodendron and Heterangium these fundamental differ- 

 ences are important and easily defined ; but in numerous 

 other instances this is not the case. To these I have 

 assigned, in my later Memoirs, the comprehensive term 

 Rachiopteris, which binds together a number of examples of 

 which the general organisation is certainlyfern-like,but which 

 signifies nothing more. As more definite groups can be 

 formed out of this very varied and comprehensive cluster, 

 such groups can be differently dealt with. With the 

 working of this method we have a good illustration in one 

 of the earliest plants that came into my hands, which I 

 had described in Part VI. of my Memoirs under the name 

 of Edroxylon, but to which I afterwards assigned the name of 

 Rachiopteris asp era. In my Part IV, I had described a 

 very distinct plant under its present name of Lyginodendron 

 Oldhaminm ; but in Part VI. I expressed my strong con- 

 viction that the former plant would ultimately prove to be 

 the petiole of the latter one. I never lost sight of this 

 possibility, but I had to wait sixteen years before I 

 obtained clear proof that my original surmise was absolutely 

 correct. This determination was an important one, because 



