138 DICITOPHTLLUM 



Genus DICTYOPHYLLUM, Lindley and Hutton. 

 [Fossil Flora, toI. ii. 1833-35, pi. civ. p. 66.] 



This generic name was proposed by Lindley and Hutton for a 

 plant originally described by Phillips from the Upper Sandstone 

 and Shale of the Yorkshire Oolite ; these authors describe the type 

 specimen, Biotyophyllum rugosum, as a " pinnatifid leaf belonging 

 to some exogenous plant." The older name, PhylUtes, having been 

 "taken as the receptacle of all sorts of leaves," the new one, 

 Biotyophyllum, is proposed for "doubtful Dicotyledonous leaves of 

 common reticulated structure." ' Subsequent writers have retained 

 the proposed name, although the discovery of sori on leaves with 

 distinct Biotyophyllum characters has necessitated an entirely new 

 definition of the genus. 



The few fragments in the "Wealden Collection add nothing to 

 our knowledge of this fern, for which we are chiefly indebted to 

 Schenk ; we may, therefore, adopt his definition of the genus ' : — 



"Folia sterilia et fertilia conformia pedato-pinnata, lacinise 

 pinnatifidse. Nervi primarii radiantes, secundarii angulo recto 

 egredientes excurrentes apice in rete soluti, tertiarii angulo recto 

 egredientes maculas insequaliter hexagonales formantes pluri- 

 seriales, costales majores, reliquse minores, omnes appendicibus 

 anastomosantibus in maculas parvas partiti. Sori per totam 

 paginam folii inferiorera sparsi, rotundi, sporangia pauca annulo 

 multiarticulato instructa, sporae tetraedricae globosse." 



Schimper,' Saporta,* and others include this genus with other 

 closely allied forms in the family Bictyopterideee. 



Saporta, in the first volume of his " Plantes Jurassiques," 

 discusses the points of difference between Biotyophyllum, Thaumafo- 

 pteris, and Clathropteris ; these difierences depend chiefly on the 

 form of the frond segments and the details of venation. In dealing 

 with small pieces of a frond it is not always easy to decide which 

 genus should be chosen. Clathropteris is, in most cases, readily 

 distinguished by the rectangular nature of the venation, but in a 



' Fosa. Flor. vol. ii. p. 66. 

 ' Fl. fosa. Grenz. Keup. Lias, p. 75. 

 2 Trait, pal. veg. vol. i. p. 617. 

 * Pal. Fran(;. vol. i. p. 325. 



