160 STUDIES IN GEOLOGY, No. 4 



impressions. Well marked slightly curved lateral veins 

 diverge from the stout, margined midvein of the pinnae alter- 

 nately, at obtuse angles (approximately right angles), and 

 terminate at the tips of the bluntly pointed, pinnatifid seg- 

 ments, of which they constitute the midribs. These give off 

 alternately, and approximately equally spaced, sub-parallel 

 veinlets, which are curved and invariably simple. There are 

 from 12 to 15 pairs of these veinlets in the sterile pinnae; 

 their spacing diminishes regularly toward the tip of the seg- 

 ment and all but the basal two or three pairs terminate in the 

 free margin of the segment. The two or at most three basal 

 pairs are slightly more curved than the rest and unite with 

 the corresponding two or three basal pairs from the sub- 

 jacent and superjacent lateral segments to form a short 

 straight ray which terminates at the head of the sinus that 

 separates the segment from its adjacent fellows. The fertile 

 pinnae are somewhat narrower than the sterile, relatively 

 shorter and broader, with more conical pinnatifid divisions, 

 separated by sinuses extending about half way to the rachis. 

 The venation is identical with that of the sterile pinnae but 

 the veins are fewer in number (8 to 10 pairs). Each veinlet 

 bears about half way between its base and apex a relatively 

 large circular sorus. The sori decrease in size distad and 

 are situated nearer the base of the veinlet, so that the 

 curved line of sori form one arc of a lens which is a counter- 

 part of the arc formed by the margin of the segment. 



The present form is a type that agrees in most particulars 

 with various Tertiary species which have been referred by 

 paleobotanists to the more or less interrelated and synony- 

 mous genera Lastrea, Phegopteris and Goniopteris. It is a 

 type met with in existing, mostly tropical ferns, that are 

 variously segregated or aggregated in the genera Lastrea, 

 Nephrodium, Phegopteris, Polybotrya and Dryopteris (As- 

 pidium). The existing species of Dryopteris number, ac- 

 cording to Christensen, upwards of one thousand species, 

 which this author segregates in ten subgenera. Most of these 



