232 mr. a. c. seward on the [May 1903, 



EXPLANATION OF PLATE XV. 



Fig. 1 . Dictyozaraites Hawelli, sp. nov. Natural size. 



2. D. Hawelli. Base of the lowest pinna shown in fig. 1 : a = surface by 



which the pinna was attached to the rachis; r = rachis of frond. 

 Enlarged three times natural size. 



3. D. Hawelli. Natural size. 



4. D. Hawelli. Portion of one of the pinnae shown in fig. 3. Enlarged 



twice natural size. 



5. D.falcatus (Morr.). x 3. 



6. D. falcatus (Morr. ). X 3. 



7. D. falcatus (Morr.). The portion shown in fig. 6 represented natural 



size. 



8. D. falcatus (Morr.). Single pinna, showing venation, x 3. 



[The specimens of D. Hawelli are from Mr. Hawell's collection, and are to be 

 deposited in the British Museum (Nat. Hist.) ; the drawings of D.falcatus 

 were made from specimen No. 52546 in that Museum.] 



Discussion. 



The President spoke of the geological interest of this paper, 

 as giving a fresh example of a fact familiar to many palaeonto- 

 logists who had devoted themselves to a single and well-defined 

 group of fossils, namely, the close similarity of the collective 

 forms belonging to that group occurring on about the same 

 geological horizon in different regions of the globe. It was often 

 a grave difficulty to decide whether the minor dissimilarities 

 were of sufficient importance to warrant the present distinctions in 

 nomenclature. The resemblances and differences no doubt both 

 existed, and neither should be ignored ; but in most cases, as shown 

 by the Author in the present instance, the resemblances were of the 

 higher systematic consequence. The great similarity between the 

 Mesozoic vegetation of the Eastern and Western regions pointed out 

 by the Author was of extreme interest; and when one bore in 

 mind the great contrast between the Permo-Carboniferous flora 

 and the Mesozoic flora of the Northern Hemisphere, and the fact 

 that the Glossojiteris-fiom had already appeared in the Southern 

 Hemisphere in later Permo-Carboniferous times, the Authors 

 views seemed to have a high theoretical significance. 



Dr. Blanford remarked that the paper was of great interest, and 

 expressed gratitude to the Author for light thrown on an important 

 portion of the world's history. The history of the genus Dictyo- 

 zamites commenced in India. Some impressions of leaves in the 

 Rajmahal Beds — shales interstratified with doleritic lava-flows — 

 were at first referred to a fern, Dictyopteris, but subsequently were 

 recognized as belonging to a Cycad and renamed Dictyozamites. 

 The discovery of the same genus in the various regions recorded by 

 the Author tended to link together the scattered occurrences of the 

 Jurassic flora in the Northern Hemisphere. But this flora — or, 

 rather, the Mesozoic flora as a whole, as defined by the Author — 

 appeared to have been of worldwide distribution, and, with the 

 possible exception of a Devonian flora, to have been the earliest 

 that was known to have been generally distributed. Representatives 

 of it had been found in South Africa and Australia, and recently 



