On the Structure and Affinities 0/ Dipteris. 



373 



given age of husband ; (b) frequency of incidence of scarlet fever at 

 different ages ; and (c) frequency of " lips " in the Medusa P. pentata. 



It is perhaps of some philosophical interest to note that solutions of 

 (i) that had escaped the analytical investigation were first obtained 

 from actual statistics which could not be fitted to any of the curves of 

 my first memoir without imaginary values of the constants. So great 

 was my confidence in (i), however, that before I discarded it I re- 

 investigated my analysis of it, and was so led to these two additional 

 solutions. 



" On the Structure and Affinities of Dipteris, with Notes on the 

 Geological History of the Dipteridinse." By A. C. Sewakd, 

 F.R.S., University Lecturer in Botany, Cambridge, and 

 Elizabeth Dale, Pfeiffer Student, Girton College, Cambridge. 

 Received May 21— Bead June 20, 1901. 



(Abstract.) 



The generic name Dipteris instituted by Reinwardt in 1828 is applied 

 to four recent species — Dipteris conjugata (Rein.), D. Wallichii (Hook, 

 and Grev.), D. Lobbiana (Hook.), and D. quinguefurcata (Baker). Dip 

 tens Wallichii occurs in the sub-tropical region of Northern India ; the 

 other species are met with in the Malay Peninsula, Java, New Guinea, 

 Borneo, and elsewhere. It has been customary to include Dipteris in 

 the Polypodiacese, and to describe the sporangia as having an incom- 

 plete vertical annulus. The authors regard Dipteris as a generic type 

 which should be separated from the Polypocliaeese and placed in a 

 family of its own — the Dipteridinae, on the grounds that (1) the 

 sporangia of Dipteris have a more or less oblique annulus ; (2) the 

 fronds possess well marked and distinctive characteristics ; (3) the 

 vascular tissue of the stem is tubular (siphonostelic), and not of the 

 usual Polypodiaceous type. 



For the material from Borneo and the Malay Peninsula, on which 

 the anatomical investigation of Dipteris conjugata is based, the authors 

 •are indebted to Mr. R. Shelford, of Sarawak, and to Mr. Yapp, of 

 Caius College, Cambridge. The fronds of the four species of Dipteris 

 consist of a long and slender petiole and a large lamina, in some cases 

 50 cm. in length; in D. conjugata and D. Wallichii the lamina is 

 divided by a deep median sinus into two symmetrical halves, but in 

 D. Lobbiana and D. quinguefurcata the symmetrical bisection of the 

 lamina is less obvious, the whole leaf being deeply dissected into narrow 

 linear segments. The sori, which are without an indusium, consist 

 of numerous sporangia and filamentous paraphyses, terminating in 

 glandular cells. The sporangia are characterised by the more or less 



