24 THE OLDER MESOZOIC FLORA OF VIRGINIA. 



ACROSTICHIDES (ACROSTICHITES Goeppert). 



Frond bipinnate or tripinnate. Pinnae linear-lanceolate, usually much prolonged. 

 Pinnules various, ovate-oblong, ovate, ovate-subfalcate, rounded, and subrhombic. 

 Middle nerve of the pinnules vanishing towards the apex, being dissolved into branches. 

 Lateral nerves depart from the middle nerve under an acute angle, the lower ones 

 forking more frequently than the upper ones. Fructification in the form of rounded 

 sporangia, covering the whole of the under surface of the pinnules and placed between 

 the nerves. 



I have defined this genus nearly as Goeppert does. It is difficult to 

 limit the character of the pinnules since they vary a good deal in the 

 sterile forms, and the fertile pinnules often differ from the sterile ones. 

 We may, however, distinguish two types in the shape of the sterile pin- 

 nules. One is ovate, or ovate-subfalcate, as shown in A. Gceppertianus and 

 A. linncecefolius. The other is broadly ovate, approaching a quadrilateral 

 and rhombic form, as shown in A. pachyrachis and A. rhombifolius. This 

 latter type is especially characteristic of the Virginia Mesozoic, as we find 

 several species showing it. 



This genus is very characteristic of the Rhaetic formation, all the forms 

 included in it being found in the Rhaetic except A. Williamsoni, which 

 occurs in the Oolite of England. The following previously described 

 species are to be included in this genus : Neuropteris linncecefolia, Bunbury, 

 from the Richmond Coal Field; Acrostichites Gceppertianus and A. princeps, 

 Schenk, from the Rhaetic of Europe; Cyclopteris pachyrachis, Goeppert, from 

 the Rhaetic of Bamberg, and Pecopteris Williamsoni, Brongt., from the Oolite 

 of England. Schimper says in his " Pal. Veg.," vol. iii, p. 476, that the 

 Cyclopteris pachyrachis of Goeppert, which in his first volume he had con- 

 sidered as a Neuropteris, ought to be placed in his section of Pecopteris 

 acrostichides, which he had limited pretty much as Goeppert had defined his 

 genus Acrostichites. He states, in addition, that the species Acrostichites 

 Gceppertianus and A. princeps, as well as Pecopteris Williamsoni, along with 

 Cyclopteris pachyrachis, might well form a group distinct from others. In 

 his description of Neuropteris linncecefolia, in which he follows Bunbury, he 

 says that this plant is probably the type of a new genus, and although he 

 had only the fructified form of the fossil as figured by Bunbury, he placed 



