THINNFELDIA. 33 



5-12 mm. latis, integerrimis, oMiquis, basi coarotata et deourrenti 

 sessilibus, approximatis, distiohis, flabellatim, venosis, nervis 

 tenuibus, subrectis ; simplicibus vel dichotomis, marginem versus 

 divergentibus." 



The specimens from tbe Lower Lias of Dorsetshire, as repre- 

 sented in PI. IV. Figs. 1-3, exhibit a considerable range in regard 

 to the size and form of the ultimate segments. The specimen 

 figured by Kurr as Odontopteria jurensis may perhaps be specifically 

 identical with the English form ; if we imagine the marginal 

 undulations of the pinnules shown in PI. IV. Pig. 3 extended 

 into distinct lobes, we should have a frond like that figured by 

 Eurr. Although it is not unlikely that the dLSerenoe between 

 Odontopteris jurensis as figured by Kurr and the English speci- 

 mens does not amount to specific difference, I prefer to adopt 

 Ettingshausen's specific designation rhowiboidalis, as the specimens 

 he figures are more nearly identical in form with those from Lyme 

 Regis. The examples of Thinnfeldia figured by Schenk from the 

 Ehsetic of Franconia as T. decurrens and T. obtusa differ in so 

 slight a degree from T. rhomloidalis that we may regard them 

 as constitutiug one type. Zigno's Italian examples referred by 

 him to Cycadopteris Brauniana can hardly be specifically dis- 

 tinguished from Thinnfeldia rhomloidalis. 



The type of plant represented by the fronds classed under 

 T. rhomloidalis had an extended geographical range during the 

 Rhsetic and Lower Jurassic periods. It is hopeless to attempt to 

 define within narrow limits the specific types of Thinnfeldia fronds ; 

 we find numerous fragments of leaves in various parts of the world 

 exhibiting a close resemblance with one another and differing in 

 what we may fairly consider unimportant details. The range of 

 Thinnfeldia extended into the southern hemisphere, where the 

 species T. odontopteroides is particularly abundant, in South African 

 Rhaetic beds, in Australia and South America ; ' in India '■' also 

 a form has been found which may be identical with the European 

 type, T. rhomloidalis. iN'athorst, in his interesting notes on 

 fossil plants in British museums, noted the very close agreement 



1 Solma-Laubacli & Steiumann (99), pi. xiv. fig. 2. 

 ■' Feistmantel (77), pla. xxxix. and xlvi. 



