580 CYCADOPHYTAN FRONDS [CH. 



of the supposed sporangia. The walls of the epidermal cells 

 are straight. The name Ctenis is applied to pinnate fronds which 

 are probably Cycadean though we have no evidence as to the 

 nature of the stem or the reproductive organs. Ctenis fronds 

 are among the largest Cycadean leaves from Mesozoic floras; 

 in Ctenis hungarica Staub the frond is said to have reached a 

 length of 2 met. and in other species the dimensions exceed those 

 of most pinnate leaves. The stout rachis bears linear or broad- 

 oblong pinnae attached at a wide angle and varying considerably 

 in size and shape; the pinnae are attached by the whole base 

 which is usually broadened and decurrent but in a few cases 

 slightly contracted (e.g. C. Zeyschneri Kac. 1 ). For some fronds 

 bearing broad and basally narrowed segments Raciborski pro- 

 posed the name Ctenidiopsis in distinction from Euctenis which he 

 applies to the typical forms. The pinnae may be long and 

 narrow reaching a length of over 12cm., or short and broad: 

 in some cases the frond would be more correctly described as 

 deeply pinnatisect; the apex of the segments is acute, bluntly 

 rounded or truncate. Several veins pass into the base of each 

 pinna and pursue a course approximately parallel to the edge 

 of the lamina ; a characteristic feature is the occasional occurrence 

 of oblique cross-connexions between the veins. It is possible 

 that in some species the pinnae had spinous margins as in the 

 pinnae of uncertain affinity figured by Fontaine 2 as Encephalar- 

 topsis nervosa from the Potomac series. Our knowledge of the 

 epidermal cells is very meagre: in the specimen represented in 

 fig. 625 the epidermal cells have straight walls and a central 

 papilla. The genus extends from Triassic to Upper Jurassic 

 rocks. 



Ctenis lunzensis Stur. 



This species, first recorded by Stur from the Lunz Upper 

 Triassic flora, has recently been examined by Krasser 3 and com- 

 pared with the Jurassic species Ctenis sulcicaulis (Phill.) (= C. 

 falcata Lind and Hutt.) and C. Potocki Rac. No figures or detailed 

 descriptions have been published. 



1 Raciborski (94) A. PI. xvi. 



2 Fontaine (89) B. p. 174, Pis. LXX. LXXII. 



3 Krasser (09) p. 113. 



