50 PTERIDOSPERMEAE [CH. 



to the leaflets of Brongniart's type. This identification is sup- 

 ported by subsequent work. The quadripinnate fronds, which 

 attain a considerable size, resemble those of recent species of 

 Davallia and other ferns, but the forking of the rachis and branches 

 of the frond is a striking feature : the pinnae may reach a length 

 of 15 cm. 1 The portion of carbonised rachis shown in fig. 405, E, 

 reveals the existence of a hypodermal reticulum like that in the 

 outer cortex of a Lyginopteris stem and the same feature is seen 

 in the more slender axis represented in fig. 404, A, at 6. 2 The 

 pinnules are usually deeply lobed and the segments may be 

 comparatively broad and blunt or narrow 3 (fig. 290, C, vol. n. 

 p. 399 ; fig. 404, A, a, B ; fig. 405, D'). The lamina has a well 

 marked dorsiventral structure: the palisade-tissue next the 

 upper surface is separated from the epidermis by small hypo- 

 dermal cells, possibly functioning as a water-storage layer, and 

 the central part of the mesophyll consists of loose aerenchyma : 

 the veins are collateral as in recent ferns and stomata occur in 

 the lower epidermis. Emergences are seen both on impressions 

 (fig. 405, D') and on petrified specimens. A striking feature of 

 the pinnules is the rounded surface caused by the revolute edge 

 of the lamina as seen in the section reproduced in fig. 404, B. 

 This character coupled with the occasional occurrence of groups 

 of short tracheal elements at the termination of the veins denotes 

 a tendency to a xerophilous habit. 



On the strength of a very close resemblance between Sphenop- 

 teris Hoeninghausi and Calymmatotheca Stangeri (fig. 408, E. F) 

 characterised by fertile pinnules bearing stellate groups of 

 small linear valves, regarded by Stur as the open lobes of an 

 indusium Zeiller included Brongniart's type in the genus Calym- 

 matotheca. The resemblance in general habit between the two 

 species extends to the presence in their rachises of the Dictyoxylon 

 form of cortex 4 . The view formerly held by some authors that 

 the valve-like appendages to the fertile segments of Calymmato- 

 theca are sporangia is incorrect: a re-examination of Stur's 



1 Zeiller (88) A. p. 82, PL vi. 



2 See also Kidston (06) B, fig. 5, p. 417; Renier (10 2 ), Pis. 60, 70. 



3 Kidston (06) B. 



4 Stur (77) p. 257, Pis. xxv. xxvi. 



