Zygopteris Grayi of Williamson . 61 
by Dr. Margaret Benson (’ll) in a species of Botryopteris , £. antiqua , in 
which they are found to be associated with the simpler monarch form of 
petiole, which in this species alternates with the larger diarch petioles. 
These remarkable organs were evidently very widely spread among the 
Primofilices ; how far they were truly homologous with the aphlebiae, so 
well known in their external form on impressions of the frond in other 
Palaeozoic Ferns and Pteridosperms, can only be determined when the 
structure of the latter has been further investigated. 
Affinities. 
There are two other species of the same type as Zygopteris Grayi y 
namely, the Z. scandens of Stenzel and the Z. Brongniartii of Renault. 
The former is so closely similar to our species that Williamson thought it 
the same, and no one has yet found thoroughly satisfactory distinctive 
characters, though the horizons are so far apart (Lower Coal Measures and 
Permian) that specific identity is improbable. Dr. Kidston (TO, p. 455) 
enumerates several points of difference, but some of these are only distinc- 
tive on the assumption that Zygopteris ( Etapteris ) di-upsilon is the petiole 
of Z. Grayi , which, as we have seen, cannot be the case, the latter being an 
Ankyropteris . From sections of Z. scandens in my possession I have not 
been able to find constant distinctions ; possibly a reinvestigation of the 
type-specimens might lead to a more definite result. It appears to be com- 
monly admitted that Z. scandens is an Ankyropteris ; this is probably the 
case, though the evidence is much less direct than is now the case with 
Z. Grayi ; here, again, a further investigation of Stenzel’s plant is desirable, 
though the close agreement with Williamson’s species leaves no real doubt 
as to the genus being the same. 
Z. Brongniartii , Ren., differs from the other species in the form of the 
stele, in which the angles are not at all prominent (Renault, ’ 69 , PL III, 
Fig. 1). This seems a well-marked distinction, though Stenzel (’ 96 , p. 31) 
thought that all three spdcies might be referable to one. There appears to 
be no independent evidence to show whether Z. Brongniartii is an Ankyro- 
pteris. There is a probability that it is so, but at present this only rests on 
the general similarity to Z. Grayi in structure and mode of branching. 
Zygopteris corrugata y on the other hand, is certainly a typical Ankyro- 
pteris y as Dr. Bertrand has shown, but differs from Z. Grayi in its cylindrical 
stele, dichotomous branching, and other points. 
The stem of the Lower Carboniferous Metaclepsydropsis duplex , of 
which a full description by Dr. Gordon (’ll 2 ) has just appeared, bears a general 
resemblance to that of Ankyropteris corrugata , the tracheides of the internal 
xylem being here also associated with parenchyma. Another Lower Car- 
boniferous plant, Diplolabis Romeri, of which Dr. Gordon has given an 
