60 ACROSTICHOPTERIS. 
Cf. Thyrsopteris Meekiana, var. angustiloba, Font., pl. lvi. ete. ; 
also Sphenopteris Mantelli, Schenk, Paleontographica, vol. xix. 
pl. xxv. fig. 6; Sphenopteris Goépperti, Schenk, loc. cit. pl. xxx. 
fig. 2; and Asplenium Dicksonianum, Heer, from the Kome beds 
of Greenland, Fl. foss. Arct. iii. pl. i. Ecclesbourne. 
Rufford Coll. 
Genus ACROSTICHOPTERIS, Fontaine. 
[Potomac Flora, U.S. Geol. Surv. Monograph, xv. 1889, p. 106.] 
Fontame has instituted this genus for certain fossil ferns 
“peculiar to the Potomac formation”; he considers that it stands 
nearest in most features to Acrostichum among recent genera. 
The genus is thus described!:— 
“Fronds, probably creeping, with very long, often flexuous, 
rachises, which seem to have been more or less succulent; pinne 
going off obliquely, long and apparently slender; ultimate pinnz 
or pinnules sub-opposite to alternate, comparatively short, and 
cut down nearly to the rachis into more or less cuneate-flabellate 
pinnules or primary segments. These are divided generally into 
cuneate-flabellate segments, which in turn are separated into 
oblong segments ending in oblong, or ovate-obtuse, or acute 
teeth; pinnules decurrent and forming a wing; nerves slender 
but distinct, flabellately diverging, forking dichotomously, and 
ending in the teeth; fructification occurring on the basal segments 
of the pinnules, in the upper portions of the frond on the upper 
one alone, in the lower portions on the upper and lower ones; 
the fructified segments, which on the lower side are covered by 
the naked sori, and seen from the upper side, especially when 
compressed on the clay, look like pods.” 
In the figures of the Potomac species of this genus there are 
several fertile specimens shown, but no detailed sporangial structure. 
Perhaps the best figure is that of a fertile pinnule of <Acrostz- 
chopteris longipennis, Font., pl. clxxi. fig. 7a. Fontaine concludes 
that ‘‘the genus in the naked sori is like Polypodium, but in 
1 Potomac Flora, p. 106. 
