AN EXTINCT PLANT OF DOUBTFUL AFFINITY. 433 



may be identical with Bowmanites Dawsoni of William- 

 son. 



It remains for us to consider the probable systematic 

 position of this genus. It is undoubtedly a Vascular 

 Cryptogam, characterised like so many other Palaeozoic 

 representatives of the group by a considerable development 

 of secondary xylem and phloem. 



Zeiller has expressed the opinion that Spkenophyllum 

 should be included in the Filicince, and in the neighbour- 

 hood of the ferns ; he institutes a comparison with Mar- 

 siliacecE and Ophioglossece. The French author draws 

 special attention to the distinct resemblance between the 

 sporangiophore of Spkenophyllum and the sporocarp stalk 

 in Marsilia. Subsequent writers have very properly 

 pointed out that we cannot well make use of this super- 

 ficial resemblance, in attempting to discover characters of 

 real morphological importance. The single sporangium of 

 Spkenophyllum differs in an important degree from the 

 elaborate sporocarp or highly specialised foliar structure of 

 Ma?-silia. The fossil genus is no doubt eusporangiate, 

 and in that respect comparable with Ophioglossum, but the 

 fertile spike of the latter differs widely from the sporangia 

 and sporangiophores of the former. Potonies * comparison 

 of Spkenophyllum with Salvinia does not render any 

 material assistance to our endeavours to assign the fossil 

 form to its true position. " We must be content for the 

 present to leave this remarkable genus in its isolated 

 position, in the hope that the extensive knowledge of its 

 organisation which we now possess may in the future afford 

 an adequate basis for comparison, when additional forms of 

 Palaeozoic Cryptogams shall have been brought to light." 2 



This conclusion arrived at by Williamson and Scott, 

 and accepted by Solms-Laubach, may perhaps be best 

 realised by making use of the term SphenophyllecE as a 

 class designation. This has been done by Schenk in 

 Zittel's Handbtich der P alee onto logic? and is the course 

 followed in a recent paper by Kidston 4 . 



1 Potonie. 2 Williamson and Scott, p. 946. 



3 Zittel. 4 Kidston. 



31 



