XVI FOSSIL ARCIIEGONIATES 585 * 



studied by Scott (j). These had Fern-hke foHage, and the 

 structure of the stem was also hke that of the h^rns, but there 

 was a marked seconcku'y thickening- (jf the stem, such as is rare 

 in hving Ferns, l>ut is known in tlie ku'ger species of Bolryclii- 

 um. The structure of tlie stem in Lyginodcndron has been 

 comi)are(l to that of Osiiiinula and tlie riymnos])erms (Sc(jtt, 

 /. c, p. 314). 



Hctcrangiuni has a monostehc stem, which agrees closely 

 with that of Glcichcnia, except for the secondary thickening, 

 pjoth Lyginodcndron and Hetcrangiuin had leaves like those of 

 a typical Fern. Unfortunately practically nothing is known 

 about their sporangia. 



Of the more Cycad-like forms may be mentioned Cycado- 

 xylon and McduUosa. While the sporangia of these forms is 

 not certainly known, it is possible that they may ha\'e been het- 

 erosporous, or even seed-bearing. (For a full account of these 

 important forms, the reader is referred to Prof. Scott's work . 

 (Chap. X, XI). 



During the past few years there have been found associated 

 \\nt\\ the Fern-like leaves of the "Ncuroptcris" and ''Alethop- 

 tcris" types, structures which appear to be real seeds, showing 

 that some, at least, of the Cycadofilices were seed-bearing 

 plants. For this reason it has been suggested that the name 

 rteridosperme?e be applied to the Cycadofilices (Grand 

 'Eury (I)). 



The peculiar genus Nocggcrathia (Potonie (j), Fig. 158) 

 is one of the few s])ore-bearing fossils, which has been referred 

 to the Cycadofilices. 



EouiSETiNE.F. (Scoff (i) ; Scztwd (j)) 



To this class are usually assigned tw^o groups of fossil plants, 

 one belonging to the Equisetace^e, and represented by the genus 

 Eqiiiscfifcs, wdiich evidently was very close to the genus Eqiii- 

 sctum, if not identical with it. The other group, the Calama- 

 riacese, differed in some respects from the living forms, and 

 there is much diversity of opinion about their real affinities. 

 The best known members of this order are the Calamitese, 

 whose anatomical structure is well known. Cormack (i) has 

 made a comparison of the structure of these with Equiscfum, 

 and comes to the conclusion that the type of structure is essen- 



