62 CYATHEACE^E. 



This species comes very near to Acrostichopteris densifolia, 1 

 Font., but differs in the shape of the pinnules ; in A. Ru/ordi 

 they are less orbicular in form, but on the other hand shorter 

 than in another Potomac species, A. longipennis* Font. 



V. 2327. PL VI. Fig. 3. 



A single sterile pinna, or possibly a pinnate frond. The re- 

 peatedly forked veins well shown, with their single branches in the 

 narrowly linear ultimate segments. Ecclesbourne. Rujford Coll. 



V. 23270 Fragments of pinnae, also what is probably part of 

 the main rachis of the frond showing the point of attachment of 

 one pinna. Close to this portion of the rachis there is a flexuous 

 structure which at first sight appears to be a continuation of the 

 former piece ; the two are, however, at slightly different levels in 

 the ironstone matrix, but in all probability both may be regarded 

 as fragments of the rachis ; on the second piece there are here and 

 there the beginnings of several lateral branches which may possibly 

 be roots. Ecclesbourne. Ruffurd Coll. 



Family CYATHEACEJ3. 



The oblique annulus and the transverse dehiscence of the 

 sporangia are the chief distinguishing features of this family. 



The genus Matonidium, Schenk, may probably be regarded as a 

 "Wealden representative of the recent genus Matonia, R. Br. ; the 

 latter, according to Baker, 3 should be placed in a tribe by itself, 

 and not united with the Cyatheacea. 



Genus MATONIDIUM, Schenk. 

 [Palseontographica, vol. xix. 1871, p. 219.] 



This genus, founded on specimens of sterile and fertile fronds 

 from the Wealden of North Germany, is thus defined : 



"Folia sterilia et fertilia conformia flabellato-pinnata, segmenta 



i Potomac Flora, p. 107, pi. xciv. fig. 4 ; pi. clxx. fig. 11, etc. 

 Ibid. p. 107, pi. clxx. fig. 10 ; pi. clxxi. figs. 1, 5 and 7. 

 3 Annals Bot. vol. v. 1890-91, p. 192. 



