190 kidston: the flora of the carboniferous period. 
and full manner which one demands in the case of genera 
founded on existing species. Notwithstanding the difficulties of 
the subject, by careful collecting and study much has been done 
in elucidating the structure and form of Carboniferous plants, 
and in some rare cases our knowledge is little less perfect than 
if we had been able to study the growing plant. Such results 
have only been attained by much study and careful observa- 
tion, and are generally the result of the united labours of 
several workers — one laying the foundation and another building 
thereon. Thus the science of palaeozoic botany has grown and, 
I doubt not, will grow. 
I. — Ferns. 
If we only consider the mere form of the frond and the 
arrangement of the veins, many fossil ferns have a considerable 
superficial resemblance to certain recent species ; still this resem- 
blance must not be regarded as affording any evidence on which 
to presume a generic relationship. The fact, however, remains 
that the same type of pinnule form and nervation which is 
found amongst Carboniferous ferns is seen amongst those exist- 
ing at present, and also the same mode of circinate vernation 
(Plate XXVI., fig. 1). 
In Carboniferous ferns the main rachis sometimes divided 
into two arms, as in C alymmatotheca bifida L. k H. sp. (Plate 
XXV., figs. 2, 3), and this dichotomous division even more 
frequently occurs in the pinnae, which are once forked, or end 
in a pair of forks. 
This character is rare in recent ferns in their native 
condition, but frequent in cultivated forms, resulting in the 
dichotomous or crested varieties of garden origin. 
Among Carboniferous ferns the principal families are the 
Sphe7iopteridece, Neuropteridece, and Pecoptei'idece. These will be 
briefly described. 
Sphenopteride^. 
Considerable latitude of character is shown by the ferns 
included in this family. The pinnules may be more or less 
oval, entire or lobed, and contracted at the base into a short 
