G. R. WI ELAND 
Neuropteris Carpentieri of Kids ton. The completely symmetrical disc 
Codonotheca, an abundant and striking fossil in the coal measure nodules 
of Mazon Creek, Illinois, ^ also appears to fall within this Neuropterid- 
Dolerophyllum alliance. It is believable that the study of these ancient 
discs must, eventually show the manner of evolution of the large vascular 
gymnosperm seeds; unless indeed the synangial hypothesis of Professor 
Margaret J. Benson for the origin of seeds accounts for the sole method. 
With this brief mention Dolerophyllum may for the present be dismissed. 
As a floral type it finds place somewhere amongst the MeduUosans, an 
immense assemblage of Paleozoic stems structurally antecedent to those 
of the Mesozoic and later Cycadophyta. Unfortunately, fructification in 
this group, though not entirely hypothetic, is about the blackest incognito 
of paleobotany. 
The Ginkgos 
A great Ginkgophyte phylum, falling but little later in geologic time, 
next arrests attention. The Ginkgos are mainly Permo-Jurassic, and 
Fig. 4. Rhipidopsis, a ginkgoid leaf which occurs in the Permian of India and Russia, 
and which strongly suggests relationship to the South American fronds mentioned in the 
text as typical in the Rhaetic. Only the outline is shown. This remarkable foliage type 
was described by Schmalhausen, .and a photograph showing the typical Ginkgo venation is 
given by Seward in his "Fossil Plants," volume 4. Here only half the natural size. 
especially exemplify the fact that the forward movement in plant evolution 
was always widespread, with the higher of the extinct forms of the successive 
periods always holding near to the persisting mean. Specialization in the 
Ginkgos seems to rise little beyond oddity of outer feature. Berry mentions 
as members of this phylum, Ginkgophyllum, Saporteae, Whittleseya, 
Trichopitys, Dicranophyllum, Rhipidopsis (cf. fig. 4), Psygmophyllum, 
Gomphostrobus, Tricophyllum, Feildenia, Phoenicopsis. There are also 
the handsome leaves called Baiera, with the staminate flowers, or Antho- 
2 On the split surface of a Mazon Creek nodule of my own, no larger than the palm of 
the hand, four complete Codonotheca discs appear, and there are parts of a fifth and sixth. 
They seem to have split off regularly, like fronds. 
