GLOSSOPTEIUS. 



51 



Apex obtuse, rounded, or obtusely pointed. Frond usually some- 

 what contracted at the base, or more rarely only very slightly 

 contracted. Midrib broad, extending to the apex, or breaking up 

 into fine reticulations at a short distance before reaching the apex. 

 Secondary nerves generally arched, more rarely oblique, reaching 

 the margin at an open angle. The obliquity of the nervation 

 varies greatly even in portions of the same frond, and the size of 

 the meshes also varies considerably. The network is as a rule 

 fairly open, the meshes being polygonal, or elongate-polygonal. 



Glossopteris Browniana varies greatly in size, shape, and in the 

 details of the nervation. An average spathulate frond measures 

 between 13 and 15 cm. in length. Other fronds are as small as 



Fig. 16. — Glossoptcris Browniana, Brong. Nervation of fronds from Australia. 

 After Zeiller. X 2. 



2 5 cm. long. Sehiinper ' has called attention to the variety in the 

 form and shape of these fronds. More recently Zeiller 3 has studied 

 in detail the variation in the nervation, variations which he 

 regards as individual and non-specific. He has pointed out that 

 the midrib is not always found to be present at the base of the 

 frond, but that it may be replaced by a group of parallel nerves, 

 in this respect recalling Gangamopteris. The obliquity of the 

 secondary nerves and the breadth of the meshes also vary greatly 

 (Text-fig. 16). The meshes may be fairly broad and almost equal 

 in size, or broader in the neighbourhood of the midrib. Or they 

 m iy be narrow, and approximately of equal size throughout. 



Schiniper (69), vol. i, p. 646. 

 Zeiller (96'), p. 3G2, figs. 8-10. 



