DESCEIPTION OF SPECIES. 55 



reaching the tips of the teeth, parallel to each other throughout their entire course. 

 Tertiary nerves strong and prominent, going off from the secondary nerves at a right 

 angle, and parallel to each other. Each tertiary nerve meets one proceeding in a 

 similar manner from the adjoining secondary nerve, about midway between the two 

 secondary nerves, and unites with it, producing at the place of junction a slight 

 departure from a straight line. The united tertiary nerves divide the space between 

 the secondary nerves into parallelograms. The tertiary nerves in turn send off 

 branches nearly at a right angle, which anastamose with each other, and with similar 

 ones coming off from the secondary nerves, and thus fill the rectangular parallelo- 

 grams with quadrilateral or polygonal meshes. Further subdivision of the nerves 

 could not be made out. 



As this plant was found only in a siliceous sandstone, the nervation 

 could not be pursued further than the branches of the tertiary nerves, and 

 these could be made out only in exceptionally well-preserved specimens. 

 The plant must have been a very large one, and could not have been in 

 the larger specimens less than 60 centimeters in length, measured from the 

 junction of the rachises of the segments to the tips of the segments, while 

 the expanse laterally of the frond was probably greater. The rachises of 

 the segments must have been very rigid and prominent, for in many cases 

 they leave deep furrows caused by their imprint in the firm siliceous sand- 

 stone. Plate XXXV, Fig. 2, represents a fragment of an abnormally large 

 segment. In this the margins do not show the teeth, hence they are not 

 preserved, but the attenuation of the secondary nerves shows that the width 

 of the fragment very nearly represents the entire width of the segment of 

 which it forms a part. Plate XXXI, Fig. 4, gives the average width of the 

 more common specimens of the full-grown plant. On this segment three 

 teeth are to be seen on the right-hand border, and one on the left-hand 

 border. Plate XXXI, Fig. 3, gives a fragment of a somewhat smaller lobe 

 or segment, in which the tertiary nerves are beautifully shown, dividing the 

 spaces between the secondary nerves into very regular parallelograms. 

 Specimens without teeth were seen 20 centimeters long, such as is shown 

 in Plate XXXII, Fig. 1. Plate XXXV, Fig. 2 a, gives a magnified portion 

 of Fig. 2 to show the details of the nervation, so far as they could be made 

 out. The stone was too coarse to allow the ultimate reticulation to be seen. 

 Plate XXXIV, Fig. 1, shows a portion of the united segments representing 

 three segments. From this some idea may be obtained of the great ex- 



