46 
SILURIAN 
PTILODICTYA FERREA- 
Plate 4, fig*. 16. 
P. fuciformis, fronde convexa crassa foliosa bifida; apicibus ex¬ 
panses. Cellulis—? 
The flat median plate which separates the upper from the 
under rows of cells, being of course in the line of greatest 
weakness, is always the one exposed in these fossils. In the 
present species it is much waved in the direction of the 
arched lines of growth. 
The fronds seem to have been about 2 inches long, and in 
this length bifurcate twice, spreading out into broad and 
wavy segments, with leafy expanded ends : the axils between 
them are obtuse. 
There is a narrower variety, if not a distinct species, in 
these rocks. We have not room to figure it. But it has 
much the same character on the whole—the irregular wavy 
surface of the basal plate, and the broad foliose frond, much 
broader in some specimens than in others. It is in limestone. 
The larger variety is in a pisolitic or oolitic iron grit, the 
same in which the Illcenus punctilio ms (pi. 1, fig. 10) is found. 
Locality. —(No. 86.)—In iron grit. (Ganesgunga ). The 
narrower variety in limestone (Nos. 1764, 931.) 
P. PLUMULA. 
Plate 4, figs. 17, 18. 
P. tmcialis, angusta, ramis ligulatis baud divaricatis ; cellulis 
rliomboideis parvis. 
A small species, with strap-shaped branches, not expanded 
or foliose, and scarcely 2 lines broad, slightly wavy, but nearly 
straight in direction, and branching at a very acute angle. 
The small rhomboidal cells show on a portion of the some- " 
what convex exterior {a in fig. 18). The ridges between 
them are simple, not elevated into tubercles or spines of any 
kind. 
Locality.— Nos. 1738, 1754, 1767, 1743, 926. 
