302 Systematic Paleontology 



sensus of opinion considers these forms as ferns, such a reference, al- 

 though probable, cannot be said to be founded upon well-authenticated 

 evidence, in fact Kerner in a recent discussion considers them cycadace- 

 ous,^ and Seward ^ makes the unwarranted suggestion of pteridospermic 

 af&nities. 



Thinnfeldia may be defined as follows: Frond pinnate, bipinnate, or 

 tripinnate. Pinnules varying much in size and shape, mostly oblong, 

 ovate-lanceolate, or oblong-obovate; decurrent and mostly confluent at 

 base, coriaceous. Eaehis broad and occasionally forked dichotomously. 

 Midvein of the pinnules dissolved before attaining the apex into many 

 simple or dichotomous laterals, which go off at a very acute angle, 

 diverging in ascending, usually several times dichotomous. Fruiting 

 forms unknown. 



The genus may be represented in the late Paleozoic, certainly there 

 are Paleozoic forms which resemble it very closely. It is, however, espe- 

 cially characteristic of the older Mesozoic. The Potomac species are 

 four in number, and are for the most part poorly defined fragments of 

 rare occurrence, Thinnfddia Fontainei Berry being of most frequent 

 occurrence as well as the best preserved form. 



Thiistnfeldia Fontainei Berry 

 Plate XL, Figs. 4-7 



TMnnfelcLia variabilis Fontaine, 1890, Mon. U. S. Geol. Surv., vol. xv, 1889, 

 p. 110, pi. xvii, figs. 3-7; pi. xviii, figs. 1-5 (non fig. 6 or Velenovsky, 

 1885. Fig. 6 is a GladopTileMs fragment of undeterminable specific 

 affinity). 

 Thinnfeldia Fontainei Berry, 1903, Bull. Torrey Bot. Club, vol. xxx, p. 443 

 Thinnfeldia variadilis Fontaine, 1906, in Ward, Mon. U. S. Geol. Surv., 

 vol. xlviii, 1905, pp. 502, 528, pi. ex, figs. 7, 8 (non Fontaine 1894, 

 1896, which are referred to CladophleMs virginiensis) . 



Description. — " Frond bipinnate or tripinnate ; rachises of the pinnae 

 stout, arborescent; pinnules lobed or toothed, with mostly ovate-obtuse 

 lobes or teeth, short, varying much in size and nature according to posi- 



* Kerner, Jahrb. k. k. geol. Reichs., Band xlv, 1896, p. 39. 

 - Seward, Fossil Plants, vol. ii, 1910, p. 538. 



