538 PTERTDOSPERMS, ETC. [f'H. 



no means improbable that many of the species referred to this 

 genus are closely allied to Palaeozoic Pteridosperms. 

 Thinnfeldia may be briefly defined as follows : 



Fronds simple and pinnatifid, pinnate or bipinnate : rachis broad and 

 occasionally dichotomously branched. Pinnules often fleshy or coriaceous ; 

 broadly linear, entire or lobed, provided with a midrib from which simple 

 or forked secondary veins are given oflF at an acute angle : or the laminae 

 may be short and broad without a midrib and traversed by several 

 slightly divergent and forked veins. 



No satisfactory evidence of reproductive organs has so far been 

 adduced. 



The genus is chiefly characteristic of Upper Triassic, Rhaetic, 

 and Jurassic floras, though it was in all probability represented 

 in Permian floras. Several species, many of which are value- 

 less, are recorded also from Cretaceous and Tertiary formations. 

 Search should be made for fertile specimens or for evidence 

 as to the association of seeds with Thinnfeldia fronds. 



Some Permian fossils from Kansas which Sellards^ has 

 made the type of a new genus, Glenopteris, appear to be 

 indistinguishable generically from leaves of Lower Mesozoic 

 age universally recognised as' typical examples of Thinnfeldia. 



Thinnfeldia odontopteroides (Morris)''. Figs. 356 — 358. 



This is a very variable species as regards the shape and size 

 of the ultimate segments and their venation. It is a type of 

 extended geographical range characteristic of Khaetic or Upper 

 Triassic rocks in Australia, South Africa, India, South America, 

 and various European localities. 



Frond bipinnate ; the broad rachis may be dichotomously branched. 

 Pinnules with a thick lamina which may be almost semi-circular in form, 

 deltoid, broadly oval or broadly linear, and often confluent at the base. 

 Short and broad pinnules occur on some fronds directly attached to the 

 main rachis between the pinnae. The longer and narrower pinnules 

 (fig. 356, C), resembling those of the Palaeozoic genus Alethopteris, have a 

 well-defined midrib, while the smaller segments are characterised by 

 several slightly divergent veins which spring directly from the rachis 

 (fig. 356, A). Epidermal cells polygonal or, above the veins, rectangular 

 in shape ; stomata, which are slightly sunk, occur on both the upper and 

 lower epidermis. Fertile specimens unknown. 



1 Sellards (00). => For synonymy, see Seward (03) p. 52. 



