OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 
159 
remains corresponding apparently to the portion f of the same figure. In my 
previous memoirs I have pointed out the fact that all these Zygopteroid bundles give 
off alternately from the exterior of each of the two parallel portions f',f" a consider¬ 
able mass of vascular tissue, each of which detached portions usually subdivides into 
two parallel secondary bundles.* The Rachio'pteris dii'plex, also described and figured 
(Part VI., ‘Phil. Trans.,’ vol. 164, Plate 55, figs. 28 and 35), exhibits the same 
phenomena, and must also be regarded as one of the Zygopteroid group ; and it is 
more than probable that my Rachiopteris insignis, figured in Part VI., Plate 16, 
figs, 19, 20, and 21, may be regarded as connecting the petiole of Rachiopteris 
corrugata, already referred to, with the Zygopteroid type. The Rachiopteris 
duplex also appears, so far as its petiole is concerned, and especially from the 
mode in which the vascular bundles of the secondary petioles are detached from those 
of the primary one, to have corresponding affinities with the same type. 
It is obvious, on the one hand, that we cannot retain both Corda’s genera of 
Zygopteris and Anaxhoropteris; and, since the type of petiole which may be designated 
Zygopteroid is the more remarkable one of the two, and appears to have several other 
Carboniferous Fern-petioles closely allied to it, it seems desirable that M. Pena tilt 
and those who wish to multiply these generic names should accept the genus Zygo¬ 
pteris and abandon that of Anachorop)teris as too ill-defined to be of any real value. 
Personally, I prefer not to multiply these generic names until we obtain a more 
definite knowledge of structural identities and differences upon which generic groups 
can be based. Hence, I shall continue for the present to use my own provisional 
term of Rachiopteris; and, since the structure of the petiole of the plant just 
described is obviously sufficiently different from that of the Anachoropteris Decaisnii 
of M. Penault to distinguish it specifically, I shall designate the former plant 
Rachiopteris Grayii, in memory of my lamented friend, Asa Gray.! 
Returning to my figures of the petioles of Rachiopteris chvplexX it will be observed 
that the two secondary bundles a, a, given off in alternate pairs from the opposite 
sides a, a of the primary petiolar bundle a, obviously supply the two secondary 
petioles y, y, giving off, in their turn, smaller bundles to a third series of branches or 
pinnules. Fig. 6 of Plate 2 of the present memoir represents a transverse section 
of a petiole of Rachiopteris Lacattii,\ for which I am indebted to Mr. Lomax, of 
* See memoir, Part VI., Plate 57, figs. 45, a" and fig. 47, m, m. 
f A further ground for abandoning M. Renault’s duplicated generic names is found in the fact that 
twice in his memoir {loc. cit., pp. 165 and 177) he considers that Zygopteris is distinguished from 
Anachoropteris by having six of the radial prolongations of the medulla, whilst Anachoropteris has only five. 
My plant just described, which certainly should belong to M. Renault’s genus Zygopteris, has but five. 
t Memoir, Part VI. (loc. cit.), Plate 65, figs. 35 d and 35b. 
§ In the memoir referred to on page 157, Professor Stenzel expresses an opinion that the petiole 
which in previous memoirs, as in the present one, I have identified with Renault’s Zygopteris Lacattii 
is really the Z, elliptica of the French author. This, however, is a mistake easily explained. In its 
middle cortex, M. Renault’s Z. Lacattii contains numeroiis gum-canals, which are not found in his 
