388 CALAMITES. [CH. X. 



of the stele forms a wide gap between the two genera. We 

 have evidence that the Calamites and Sphenophyllums were 

 probably descended from a common ancestral stock, and it 

 may be that in Archaeocalamites, some of the Sphenophyllum 

 characters have been retained ; but there is no close affinity 

 between the two plants. 



On the whole, considering the age of Archaeocalamites and 

 the few characters with which we are acquainted, it is probable 

 that this genus is very closely related to the typical Calamites, 

 and may be regarded as a type which is in the direct line of 

 development of the more modern Calamite and the living 

 Equisetum. Weiss ^ includes Archaeocalamites as one of his 

 subgenera with Galamitina and others, and it is quite possible 

 that the genus has not more claim to stand alone than other 

 forms at present included in the comprehensive genus Calamites. 



The student will find detailed descriptions of this genus in 

 the works which have been referred to in the preceding pages. 



1 Weiss (84), p. 56. 



