IHINNFELDIA. 29" 



There is considerable confusion in regard to the terminology 

 applied to various Ehsetio and Jurassic fronds, or portions of 

 fronds, which hear a close resemhlance to Ettiugshausen's 

 Thinnfeldia rhomhoidalis, the type -species of the genus. The two 

 best known and widely distributed species of this genus are 

 T. rhomboidalis, with which may be included several forms 

 designated by authors as distinct species, and T. oiontopteroiies 

 (Morr.). The latter type, originally described by Morris in 

 Strzelecki's book on New South "Wales as Pecopteris odon- 

 topteroides,^ is characteristic of Ehsetic rooks in South America, 

 South Afi'ica, and Australia. The examination of several 

 specimens of this species from the Stormberg beds of the Cape 

 has convinced me that the distinction between Morris's species- 

 and Ettingshausen's European species is not always well defined. 

 There is, moreover, a striking agreement between some of the 

 specimens described by Nathorst from the Rhsetio of Scania as 

 species of Ptilo%amites'^ and the southern species of Thinnfeldia. 

 I have no doubt that Ptilommites and Thinnfeldia represent closely 

 allied genera, which, indeed, may not be generically distinct. 

 Another designation that has been employed in the determination 

 of fronds identical in habit with Thinnfeldia is Lotnatopteris. This- 

 name was instituted by Schimper '^ for a plant previously described 

 by KiuT as Odontopteris (?) jurensis,^ and by Quenstedt as Neu- 

 ropteris limbata. In 1861 Zigno instituted the term Cycadopteris 

 for certain Italian specimens which were afterwards included by 

 Schimper under his genus Lomatopteris. Saporta,^ Zeiller,* and 

 others have retained both Lomatopteris and Cycadopteris in 

 addition to Thinnfeldia, and the feature noticed by these authors as 

 distinctive of Cycadopteris is the presence of a thicker border in 

 the lamina of the ultimate segments. This characteristic margin is 

 well shown in the Dorsetshire specimens represented on Plate IV. ; 

 it is not formed by the overfolding of the edge of the pinnule, 

 but is simply a darker (cuticularised) border. The difflculty, 



1 Seward (03), p. 62. 

 » Nathorst (7»). 

 ' Schimper (69), p. 472. 

 « Kurr (45). 



5 Saporta (73). 



6 Zeiller (00), pp. 93, 98. 



