28 



GROUP RELATIONSHIPS 



was described as '^>S'. elegans" by Brong- 

 niart in 1839) was first described in 

 adequate detail by Kidston in 1905 from 

 a specimen found at the Great Coal- 

 ball horizon in England (the same as 

 Mazocarpon sliorense). The peduncular 

 steles described within the stem were 

 apparently not similar to those in speci- 

 mens of M. shorense, and no comparison 

 has been made between the structures 

 of the two. Kidston 's description was 

 drawn from sections of only two ped- 

 uncles, and it seems that the Colne 

 specimen with many peduncular steles 

 provides a more accurate picture of 

 the variation possible in these structures. 

 Apparently none of Kidston 's original 

 sections passed directly through a zone 

 of the stem which bore numerous cones. 

 It would seem that the differences be- 

 tween the peduncular steles of Kidston 's 

 specimen are easily reconciled with those 

 shown by Mazocarpon now that both 

 solid and medullated steles are known 

 in the later genus. 



Mazocarpon oedipternum shows that 

 Mazocarpon may have both solid and 

 medullated steles within the limits of 

 the same species; the Colne Sigillaria 

 shows that both types of peduncular 

 steles may even be formed within the 

 same plant. The presence of a solid 

 type of peduncular stele in Kidston 's 

 original specimen of Sigillaria elegans 

 and in Graham's Sigillaria approximata 

 is not discordant with the belief that 

 Mazocarpon type of cones were borne 

 hy Sigillaria. In the absence of conflict 

 in these more precise characters and in 

 the agreement of other more general 

 information, the fact of a generic over- 

 lap seems sufficiently founded. On the 

 other hand, there is no very convincing 

 specific agreement in peduncular struc- 

 tures of any of the species of Sigillaria 

 or Mazocarpon. This is not surprising 

 in view of the few descriptions of Mazo- 

 carpon and other sigillarian cone ped- 

 uncles which have been published. The 

 inherent variation in peduncular struc- 

 ture may in itself be regarded as a 

 generic character, and such variation in 

 any event renders specific correlations 

 more difficult. This emphasizes the 

 necessity of classifying in separate 

 groups the fossils identified by charac- 



teristics of their cones and those identi- 

 fied chiefly on characteristics of their 

 stems. In each group, other more stable 

 characteristics are present and serve 

 best as means of specific discrimination. 



RELATION OF MAZOCARPON 

 AND SIGILLARIOSTROBUS 



In view of the similar relationship 

 which has been suggested between both 

 of these genera and the genus Sigillaria 

 it may be expected that the relationship 

 between Mazocarpon and Sigillariostro- 

 hus is particularly intimate and that 

 generic synonymy might exist. The 

 present evidence favors this interpreta- 

 tion; nevertheless, if we are to main- 

 tain precision in the application of nom- 

 enclature, it is impractical to assign all 

 of the species classified in both groups 

 to any one generic group. On the other 

 hand, it would seem justified to unite 

 them in some larger group, such as a 

 tribe. As stated above, Mazocarpon is 

 more precisely definable and is presuma- 

 bly therefore a more satisfactory taxo- 

 nomic group. 



Miss Benson (1918) has previously 

 discussed some of the evidence for be- 

 lieving Mazocarpon and Sigillariostrohus 

 very closely related and has compared 

 Mazocarpon shorense with Sigillarios- 

 trohus ciliatus, S. rhomMbracteatus, S. 

 tieghemi, etc. In view of the additional 

 information made available in Mazo- 

 carpon oedipternum, the relationship 

 between the two genera may be reexam- 

 ined with reference to a few important 

 characters, and further discussion may 

 be, presented concerning certain species 

 of Sigillariostrohus, chiefly those de- 

 scribed since Miss Benson's paper ap- 

 peared. 



The diagnosis of Sigillariostrohus is 

 still subject to differences in interpreta- 

 tion. By many the name is used to 

 designate cones or cone fragments which 

 are supposed to correlate with Sigillaria. 

 But a scientific nomenclature may not 

 be based on suppositions, and at least 

 some of the specimens assigned to this 

 genus in the past must be considered 

 problematic or identifiable only to some 

 group having broader affinity than 

 Sigillariostrohus. 



A cardinal point in the identification 

 of Sigillariostrohus is the pedunculate 



