Vol. 59.] OCCURRENCE OF DICTYOZ AMINES IN ENGLAND. 217 



pinna is slightly over 2 centimetres in length and has a breadth of 

 4 millimetres ; the veins, not always accurately represented in 

 Eeistmantel's plates, are clearly defined. Most of the leaflets are 

 imperfect, but in a few cases (PI. XV, fig. 6) one is able to see that 

 they were attached to the rachis by a small portion of the lamina 

 occupying an approximately-median position on the basal end ; the 

 edges of the base are very slightly lobed. 



On the same porcellanous slab numerous fragments of other 

 fronds occur, which I am unable to distinguish from Williamsonia 

 pecten. 



The next contribution to our knowledge of Oldham's genus was 

 made by Dr. Yokoyama, 1 who recorded the occurrence of the Indian 

 type at Ozo in the Province of Kogaand at Ushimari in the Province 

 of Hida in Central Japan. Most of the Japanese specimens are 

 referred to a variety of the Rajmahal type— Dictyozamites indicus, 

 var. distans ; but a new species was instituted by Yokoyama, under 

 the name D. grossinervis, for a form of pinna characterized by a 

 coarser form of reticulation. 



In 1889 Prof. Nathorst published a paper ' Sur la Presence du 

 Genre Dictyozamites, Oldham, dans les Couches jurassiques de Born- 

 holm.' 2 The specimens, collected by Herre A. E. Carlson in 1885, 

 in the neighbourhood of Hasle in Bornholm, were named by Prof. 

 ISTathorst Dictyozamites Johnstrupi. This species agrees in the habit 

 of the frond with the Indian form, but differs slightly in the shape 

 of the pinnae and in their manner of attachment to the rachis of 

 the frond. Mr. HaweH's discovery at Marske affords proof of the 

 occurrence of Oldham's genus in a second European region of rocks, 

 of approximately the same geological age as those of Bornholm. 



Distribution of the Genus Dictyozamites in the Jurassic 



Period. 



Dictyozamites falcatus (Morr.) Raj mahal Series of India. 



Dictyozamites falcatus (Morr.), var distans, \ „ , ,. 



Yok j * 



Dictyozamites falcatus (Morr.), var. qrossi- ] ^ . , T 



nervis,Yo\* j Central Japan. 



Dictyozamites Johnstrupi, Nath Bornh olm. 



Dictyozamites Hawelli, sp. nov England (Marske, E. Yorks). 



In the absence of reproductive organs it is impossible to speak 

 with confidence as to the affinity of the genus. It has long been 

 customary to include fossil fronds, which agree in their pinnate 

 method of branching and in the form and arrangement of the pinnae 

 with the leaves of modern Cycads, in the class Cycadales. The 

 monotypic Australian genus Boivenia is the only existing Cycad in 



1 Yokoyama (90) pp. 53, 55, pi. vii, fig. 10, pi. x, figs. 4-10, & pi. xi, fig. 5. 



2 Nathorst (89). 



3 I have reduced Dr. Yokoyama's species D. grossinervis to the rank of a 

 variety, as the small fragments with the coarser type of venation seem to me 

 to be more appropriately distinguished by the term grossinervis, used as the 

 designation of a variety, than as defining a distinct species. 



q2 



