1528 CORMOPHYTA. 



Rhiptozamites from the Jurassic of Siberia, to which Nceggerathiopsis 

 of the Lower Gondwanas of India, the Hawkesbury beds of Australia, 

 and the Rhaetic of Honduras, is closely allied, if indeed it be gen- 

 erically separable. It is known by specimens which appear to be 

 leaflets of a pinnate leaf, and are of an elongate form with forked 

 radiating veins which do not converge towards the summit. 



Genera founded on the Fructification. — The name Cyca- 

 dospadix has been applied to the female fructification of Cycads 

 from the Lower Lias and Corallian closely resembling that of Cycas. 

 Cones from the Lias to the Wealden have been described as Zamio- 

 strobus and Beania ; while seeds, ranging from the Keuper to the 

 Wealden, are known as Cycadeospermum. 



Genera founded on Stems. — Stems of Cycads are of not un- 

 common occurrence, especially in fresh-water deposits, and are 

 locally known to the quarrymen of the south of England as " fossil 

 birds'-nests." According to the arrangement of Count Saporta they 



may be classified as follows : 

 Bolbodiu?n, from the Lias and 

 Corallian ; Cylindropodium, 

 from the Lower Lias and Up- 

 per Jurassic ; and Mantellia 

 (fig. 1397), also known as 

 Cycadoidea or Clathropodium, 

 from the Upper Jurassic and 

 Wealden, which is especially 

 common in the " dirt-bed " of 

 the Isle of Portland. Other 



Fig. 1397.— Stem of Mantellia megalofihylla ; q1 - prn( , r o n m no - frnm rhp Turns 

 from the Purbeck of the Isle of Portland. Re- Stems, ranging trOHl tUe J UraS- 



duced - sic to the Lower Greensand, 



have been described by Mr 

 Carruthers under the name of Bennettites ; the associated fructifica- 

 tion differing in several respects from that of existing types. The 

 preceding forms have comparatively short stems, but in Platylepis, 

 of the Lias, and Fittonia and Buckhmdia, of the Upper Jurassic 

 and Wealden, the stems may attain a height of several feet. 



Here we may notice the remarkable genus Williamsonia, ranging 

 from the Rhaetic to the Jurassics of Europe, in regard to the serial 

 position of which there has been much discussion. It is based on 

 the fructification, which in some cases is found attached to stems 

 with spirally arranged leaves. It has been suggested that this plant 

 may belong to the Dicotyledons, while Mr J. S. Gardner considers 

 that its affinities are with the monocotyledonous Pa?idanacece ; but 

 it appears quite possible that it may really prove to be an extremely 

 aberrant Cycad. This genus is also found at the base of the Upper 

 Gondwanas of India. 



