196 ME. H. HAMSHAW THOMAS A]SD MISS N. BANCROFT ON 



looking sometimes like cells, but probably representing the tliin places above the 

 ends of the guard-cells. More or less surrounding the stomata at the sides are two 

 large subsidiary cells, often somewhat tliickened. The above description applies both 

 to (a) pinnate compound fronds, e. g. Ttilophyllum, Otozamites, DictyozamiteSy and 

 Zamites, some of which are known to have belonged to plants bearing flowers of the 

 WiUiamsonia type, and to (6) simple fronds, e. g. TceniopterlSy which is usually entire, 

 and Anomozamites, which is usually pinnately lobed. Eronds of the latter have been 

 found to belong to plants with a peculiar type of Bennettitalean flower {Wielandiella). 

 There are then, strong grounds for regarding the type of cuticular structure described 

 above as characteristic of the fronds of the Bennettitales. 



The cuticles of the second series, which includes the genera Nilssonia, Cteiiis, and 

 TtilozamiteSj are sharply marked off from those described above. In this section the 

 cuticles may be thin (as in the Nilssonias) or very thick ; they appear to have been 

 formed from cells of elongated, rectangular, rounded, or fusiform shapes, with straight 

 walls. The stomata are on the under side of the leaves and exhibit no regular 



f 



arrangement, the guard-cells are somewhat deeply sunken, and the six or eight 

 thickened subsidiary cells which surround them often form a somewhat overarching 

 canopy. The guard-cells are hemispherical or spindle-shaped, they are only thinly 

 cuticularised, and definite lamellar thickenings are seldom seen. 



The cuticles in this group do not agree with one another so closely as do those in the 

 Bennettitalean group, Ctenis and Ffilozamites are similar, but the Nilssonias are not so 

 closely related. The fronds were variously shaped, those of Ctenis and of some species 

 of Nilssonia were large and pinnate, JPtilozamites was bipinnate, while the fronds of 

 Nilssonia orientalis were simple and often entire or only slightly lobed. It may be 

 noticed that the thickness of the cuticle in these forms bears an apparently definite 

 relation to the size of the frond. Of the bipinnate Ftilozamites no complete fronds have 

 been obtained, but they were probably of considerable size, their cuticles were very 

 thick ; the large fronds of Ctenis, and also of the Lower Estuarine form of Nilssonia 

 mediana had cuticles of considerable thickness. The smaller fronds of Nilssonia compta 

 from Gristhorpe had thinner cuticles, while the much smaller entire fronds of Nilssonia 

 orientalis had very delicate cuticles. We see no such gradation among the Bennetti- 

 talean group. We know very little about the affinities of the plants which bore the 

 fronds placed in this second section. Prof. Nathorst has found fronds of Nilssonia 

 pterophylloides associated with numerous seed-like bodies in such a w^ay as to render 

 their original connection probable, but the stems and reproductive organs of the other 

 species and genera are as yet quite unknown. Though it is quite possible that some 

 of these plants were closely related to the recent Cycadales, there is as yet no definite 

 evidence in support of this view. It may be convenient if we institute the name of 

 NiLSSONiALES for the group of fronds which has just been described. 



