G. B. Wieland — Williamsonian Tribe. 



435 



which lies our great hope of future discovery not only of crit- 

 ical anatomic features, but eventually of the ecology and larger 

 history of the Cycadophyta. In short the narrow structural 

 range of the silicified trunks, well nigh expressahle in the terms 

 of a single genus, is only what might be hypothesized from the 

 features of a single species like Cycadeoidea dacotensis, were 

 it the only known form. These are but the stereotyped termi- 

 nal forms of a side branch from a great plastic and dominant 



Fig. 1. 



Fig. 1. Map of the globe showing the principal Rhat-Liassic localities 

 yielding Williamsonian foliage and fructifications. Various scattered Liassic 

 and other mid-Mesozoic areas in Europe, America, Madagascar, and elsewhere, 

 are not indicated ; though some of these, as for instance the Liassic of Italy 

 (Zigno), yield important fossil floras. 



This map as modified from Seward (26) shows the notable chain of local- 

 ities on the Pacific coast of the Americas with the newly discovered Oaxacan 

 region in the same latitude as, and on the exact opposite side of the globe 

 from its nearest analogue, in the Rajmahal Hills and Gondwanas of India. 



[References : Localities 1-13 in Seward (26) ; 14 cf . (3), 15 cf. (22) and (27), 

 16 cf. (11), 17 cf. (13).] 



precursor race unquestionably including the vast bulk of 

 Cycadophytean vegetation from the earliest Triassie to mid- 

 Cretaceous times. We thus see in the Williamsonise the 

 representatives of a vast Mesozoic plexus derived from a Paleo- 

 zoic quasifern ancestry in which pro-angiospermous characters 

 are ever surely and obviously engrafting themselves. And we 

 conceive this plexus to contain many discoverable forms of 

 great variety in size, foliage, branching, and floral types dis- 



Am. Jour. Sci.— Fourth Series, Vol. XXXII, No. 192. — December, 1911. 

 32 



