DESCRIPTIJX OP SPECIES. 31 



Plate XII, Fig. 2. The lower pinnules on this specimen, Plate VIII, Fig. 2, 

 show in a striking manner the peculiarly elegant shape which the pinnules 

 of this plant often assume. I have on this account given an enlarged figure 

 of one of these pinnules, Plate VIII, Fig. 2 a, which at the same time shows 

 the nervation. The narrowing of the ultimate pinnae towards their base is 

 well shown in Plate XII, Fig. 1. I have given a series of figures represent- 

 ing the gradations of the ultimate pinnae in passing into simple pinnules 

 towards the top of the frond. Plate XII, Fig. 2, represents the pinnules 

 nearly completely united. Plate VIII, Fig. 3, represents a part of the frond 

 where the pinnae are much diminished in length and width, and where a 

 rounded lobing only is shown, while towards the summit of the specimen 

 the pinnae are nearly reduced to pinnules. In Plate XIII, Fig. 1, the pinnae 

 are now reduced to simple pinnules, the lowest ones showing still an undu- 

 lation on the margin. These pinnules are more elongate-falcate, and stand 

 more nearly perpendicular to the rachis than the normal pinnules of the 

 middle and lower parts of the plant. In fact they are so much unlike these 

 that if they were seen only in isolated specimens, they would be considered 

 as belonging to a different species. I did so consider them until I was forced 

 by the finding of passage forms, showing a complete gradation of one into 

 the other, to unite them in one species. Plate VIII, Fig. 3 a, represents a 

 magnified pinna of the lower part, of Fig. 3 ; 3 b represents a magnified pinna 

 of the upper part of the same. 



Plate XIII, Fig. la, gives a magnified pinnule of Fig. 1, where the 

 seeming pinnules are really equivalent to the pinnae of the lower parts of 

 the plant. Plate XIV, Figs. 1 to 2, represent portions of fertile fronds. All 

 the pinnules are granulated. Plate XIV, Fig. 2 «, gives a magnified portion 

 of Fig. 2, and la, a magnified section of Fig. 1. It will be borne in mind 

 that in most of the figures of the plants given in this memoir all the details 

 are not represented in every portion of the plant when they are similar to 

 those given in the parts which are completed. Plate XI, Fig. 3, represents 

 a portion of a pinna magnified twofold, in which the fructified pinnules are 

 semicircular and opposite, and also united for some distance. These are 

 unusual features in this species. Plate XIII, Fig. 2, gives the upper part 

 of a fertile frond, where the pinnce are tending to pass into simple pinnules. 



