HOOKER LECTURE, 1922. 229 
data on which diagnoses rest stand in the way of precision and thoroughness 
of comparison. The genera Dictyophyllum, Thaumatopteris, Camptopteris, 
and Clathropteris are the best-known members of the Camptopteridinæ ; the 
genus Hausmannia, as Halle has recently shown, may safely be more closely 
associated with /ipteris. 
Dictyophyllum is represented by many species, not always easily distin- 
guishable, ranging from Upper Triassic to Lower Cretaceous floras. It is 
characterised by large webbed fronds, with reticulate venation, often borne 
on long petioles sparsely scattered on creeping rhizomes. Illustrations and 
descriptions published by Nathorst and by Zeiller show that the fronds of 
some forms must have exceeded in size those of the largest Dipteris, reaching 
a span of about 2 metres, with individual pinnæ attaining a length of 1 metre. 
There is considerable range in the lobing of the pinnæ, in the form of the 
ultimate segments, and in the size of the fronds. In some of the Rhætic 
species the petiole forked into two equal arms curved outwards and slightly 
inwards like the limbs of an inverted Moorish arch, each bearing apparently 
on the outer side, but actually on the twisted inner side, numerous spreading 
pinne. An untwisted /ictyophyllum, but for the webbed and retieulately 
veined lamina, would be practically identical with a frond of Matonia 
pectinata. The sori are crowded and often confluent; the annulus is incom- 
plete. The sporangia are larger, fewer in each sorus, and produced more 
spores than in Dipteris. Mr. Hamshaw Thomas has recently shown that in 
the Jurassic species Dietyophyllum rugosum the sporangia are not in definite 
sori but scattered over the surface of the frond, agreeing in this respect 
more closely with the recent genera Platycerium and Cheiropleuria than 
with Dipteris. In the Rheetic species the sori are of the Simplices type. 
Mr. Thomas concludes that Dictyophyllum and other related Mesozoic Ferns 
“should be considered as closely allied to the modern Dipterid ferns.” 
Thaumatopteris. This genus is similar in habit and range to Dietyophyllum 
and may perhaps be regarded as a subgenus. For our immediate purpose 
the differences between the two types are unimportant. 
Camptopteris. In the Rheetie species, C. spiralis, Nath., from the South 
of Sweden, the spiral twisting of the arms of the petiole is carried further 
than in Dictyophyllum, with the result that the long and narrow pinne are 
attached along a spiral line. In another species, C. serrata, Kurr, the habit 
of the frond conforms to that of Matonia pectinata. | 
Clathropteris. The serrate strap-shaped pinnæ, which may reach a length 
of 80 cm , are given off from two arms of the petiole; at the base the laminæ 
and the fan-like group of pinne are united and the main ribs form a Matonia- 
like pattern. The rhizome agrees closely with that of Dietyophyllum. 
Hausmannia. The more completely webbed fronds of this genus are in 
some species indistinguishable in habit, as in venation, from those of some 
examples of Dipteris. A fortunate discovery of well-preserved fertile 
