SECTIONAL TRANSACTIONS.— K. 413 



or less rectangular Dicotyl-like network through a ' Phlebodium '-like arrangement, 

 as in D. quinquefurcata (Baker) may occur. The sori are abundant, scattered, naked, 

 as in Polypodium ; sporangia with paraphyses and incomplete more or less vertical 

 annulus. Seward and Miss Dale give a detailed account (recent and fossil) of the 

 Dipteridince to date. 



The Ballypalady specimen consists of an incomplete stalked frond. The stalk 

 is 10 cm. long 1 mm. wide. The segments of the lamina are 7 cm. long, 1.5 cm. wide. 

 The whole frond is 16-17 cm. long and 10-12 cm. wide. The bifurcation of the stalk 

 at its distal end is clearly observable, accompanied by the passage, into the two 

 halves of the lamina, of the vascular bundles. One half of the fossil frond is very 

 incomplete, but the lobes or segments of the other half are clearly observable and 

 show well the repeated forking of the veins. The fossil is a sterile ' impress ' only, 

 and there is only here and there a trace of the reticulum of smaller veins. Of the 

 recent species of the genus the fossil comes nearest to D. conjugafa, and seems to fit 

 in between normal fronds of this species especially as figured by Kunze in Diels's 

 article, and the abnormal form figured by Seward. This likeness is in keeping with 

 one's expectation. The nearer the fossil is in time to the living form the closer the 

 resemblance to be expected. Our fossil, small compared with the fine specimens in 

 the ' Levinge ' fern herbarium in this museum, may be named Dipteris conjugaloides. 

 The Dipteridince are first recognisable in the Keuper (Uppermost Triassic), reach their 

 maximum development in the Jurassic with world-wide distribution, excluding 

 S. America, S. Africa, and (curiously) E. Indies, and, as Gothan points out, already 

 show signs of waning in many forms in the Wealden (Lower Cretaceous). Thus 

 Hausmannia, a member of the group, is represented by, mostly, small forms only. 

 One Jurassic species of this genus is recorded from the Upper Oolite or Kimmeridge (?) 

 of Sutherland. Gardner describes fragments of leaves from the Eocene beds of 

 Bournemouth as Podoloma polypodioides and P. affne. Seward notes the close 

 resemblance of the venation as figured by Gardner to that of the venation of a Dipteris. 

 Gardner's Fig. 6, quoted by Seward as D. polypodioides, is most like D. conjugata 

 in venation, &c., but is ' probably of a different (unnamed) species ? ' according to 

 Gardner. If, as seems so, Seward's reference of Podoloma to the Dipterids is correct, 

 the Bournemouth plants lend support to the view that the Malay Dipterids occurred 

 in Britain in the Tertiary as well as in Ireland, as indicated by the Ballypalady 

 fossil. 



The gap between the fossil Dipterids of the British Isles and the living forms of 

 the East Indies is in part bridged by the fossil beds of Bohemia. Velenovsky dis- 

 covered a fern in the Cretaceous of Bohemia in which he saw a likeness to Platycerium 

 bi forme Hook. Krasser in 1896 noted its resemblance to a Dipteris and named the 

 fossil Dijiteriphyllnm creiaceum (Vel.) Krasser. 



Through the kindness of Dr. F. Nemejc I have received photographic illustrations 

 of the Velenovsky fossil. The agreement with the Irish fossil in all ascertainable 

 features is so pronounced as to indicate more or loss complete identity. 



The beds in Bohemia which yield fossil Dipteris also contain the anomalous 

 Dicotyledon Dewalqnea, of which Irish forms from the Washing Bay core have been 

 recorded. I have also found, but not previously recorded, this genus in the Bally- 

 palady beds. 



As Dewalquea and fossil Dipteris (e.g. Dipteriphyllum) are essentially Cretaceous 

 in their latest forms as recorded from Bohemia, Belgium, America {Dewalquea), their 

 presence in Ireland in the Tertiary is of added interest. 



30. Prof. D. Ellis. — The Reproductive Methods and the Internal Structure 

 of the Sulfhur Bacteria. 



The results are the outcome of the detailed study of Thiophysa volutans. Hitherto, 

 with one exception, only reproduction by fission has been known for the organisms 

 of this group. In Thiophysa volutans, under certain conditions of equilibrium, repro- 

 duction by budding (similar to yeast-budding) prevails for a limited period, the 

 organism increasing enormously in point of numbers. Lender certain other conditions 

 eiidospores make their appearance, thus forming resistant reproductive cells. 



The internal structure of Thiophysa volutans is discussed, including a consideration 

 of the purple colouring matter, the sulphur globules, cytoplasm. &c. 



