152 SPHENOPTERIS. 



venation might be described almost equally well as agreeing with 

 the Sphenopteris or Cladophlelis type ; in the larger pinnules there 

 is a definite midrib giving off forked secondary veins at an acute 

 angle, but in the smaller deltoid segments the venation is more 

 spreading and approximates more closely to that of Sphenopteris. 

 The fertile segments bear sporangia covering the lower surface. 

 The rectangular disposition of the pinnae and pinnules and the 

 rather indefinite ragged appearance of the delicate and finely 

 crenulate segments give to this species a characteristic habit. 



The description of the stem and of the fertile segments is taken 

 from Schenk's diagnosis * of Acrostichites princeps ; neither stems 

 nor fertile segments have so far been recognized in association 

 with the English specimens. 



In his valuable notes on the English Jurassic plants, Nathorst 2 

 has expressed the opinion that the specimens for which Leckenby 

 instituted the new specific name Sphenopteris modesta are identical 

 with Presl's Rhaatic species S. princeps, afterwards referred by 

 Schenk to the genus Acrostichites and fully described and 

 illustrated in the Flora of the Rhcetic Beds of Franconia. The 

 figures given by Schenk represent a type of frond which appears 

 to be identical with Leckenby's Sphenopteris modesta. I cannot 

 detect any discrepancies which justify a specific separation of the 

 two sets of specimens ; in spite of the fact that one plant is from 

 Rhaetic and the other from Lower Oolitic rocks, Nathorst's 

 determination has therefore been adopted. 



Nathorst points out that the generic name Acrostichites, chosen 

 by Schenk on the strength of the fertile pinnule having the 

 under surface covered with sporangia, is not very suitable, as 

 the same manner of occurrence of sporangia is met with also in 

 species of Aspidium, and other recent genera. "We may add that 

 the same mode of occurrence of crowded sporangia occurs also in 

 Todea, as illustrated by the Jurassic species formerly referred to 

 Acrostichites and now placed in the genus Todites. Raciborski 3 

 records Sphenopteris princeps from Cracow, and places it in the 

 Osmundaceae under the name Todea princeps. 



1 Schenk (67), p. 46. 



2 Nathorst (80 1 ), p. 56. 



3 Raciborski (91), p. 4. 



