OE THE EOSSIL PLANTS OE THE COAL-MEASURES. 
219 
hend all these fragmentary stems and petioles in a common group, such as Rachiopteris , 
without pretending to assign to that term a true generic value, and then to subdivide 
the group into subsections, according as the specimens appear to have features in 
common, such as that of Zygopteroides, Stauropteroides , &c. By this plan we avoid 
the absurdity of creating numerous meaningless genera, each one of which is only 
represented by fragmentary parts of plants. Hence I would designate the plant which 
I have just described Rachiopteris corrugata, and include it, along with M. Be vault’s 
Zygopteris Rrongniarti and Anachoropteris Recaisnii *, in the subgroup of Anaclioro- 
pteroides, the distinguishing features of this group being the possession of a central 
vascular axis which forms a virtually closed cylinder surrounding a cellular medulla — two 
features in which these stems of Ferns approach very closely to those of the type of 
Lepidodendron represented by Lepidodendron Harcourtii. In the adoption of the above 
plan of classification I have benefited by some valuable hints from Dr. Hooker, who 
kindly gave me the advantage of his vast experience in the study of systematic botany. 
It has long been noticed as a remarkable fact that whilst the Oolitic ferns of the 
Gristhorpe shales so frequently exhibit sori attached to their fronds, ferns with sporangia 
in situ are rare in the true Coal-measures. Brongniart long ago figured a solitary 
leaflet of Neuropteris flexuosa which affords indications of sori upon its surface (Veg. 
Foss. pi. 65. figs. 3, 3 a, & 3 b). Corda figured two examples, under the names of 
Senftenbergia elegans and Hawlea pulcherrima f , in which these conditions exist ; and 
more recently M. Benault has described two other examples under the names of 
Rotryopteris dubius and B. forensic ? J, in which also the sporangia are found attached 
to a branching axis. One of these species was from Autun, the other from St. Etienne. 
Prof. Schimper has figured a fertile frond of Palosopteris Hibernica (Traite de Pal. 
Veget. vol. i. pi. xxxvi.). Mr. Bailey has represented the same fern in his £ Figures of 
Characteristic British Fossils ’ (pi. xxviii. fig. 1), and, still more lately, Mr. Carruthers 
has figured the same plant with fertile pinnules in the ‘ Geological Magazine,’ vol. ix. 
No. 2. The latter Memoir also contains figures and descriptions of some detached 
sporangia from the Oldham deposit, which its author believes to be of the type found 
in the recent Hymenophylle®. 
During my long-continued researches I have failed to discover a solitary fern-frond 
in the Coal-measures of Lancashire, Yorkshire, or Durham in which sori were to be seen 
in situ , and in my large collection of sections I have met with extremely few traces of 
detached sporangia. Here and there a fragment of an annulus has been observed, but 
too imperfect for identification with any special type § . Mr. Butterworth has been 
* Annales des Sciences Naturelles, 5 e serie, Bot., t. xii. (Cahier No. 3). 
f Elora de Yorwelt, Taf. lvii. J Annales des Sciences Nat., 6 e serie, Bot., tome i. pi. 10. 
§ This remarkable fact indicates that the fossil fronds have been exposed for a long time to the action of 
water before they became buried in silt and mud. At the same time, remembering how common fern-fronds 
are in the coal-shales, and what myriads of sporangia they must have set free, it is strange that we do not find 
detached ones more abundantly than is the case. (Since the above remarks were penned, I have obtained 
additional examples of such sporangia from Messrs. Bums and Spenceb, of Halifax. — June 2 , 1877.) 
