168 
VINE : CARBONIFEKOUS POLYZOA. 
previously referred to F. membranacea as some resemblance exists 
between the two species if the central stem is absent in the frag- 
ment : otherwise there are few features in common between Fenes- 
tella and Ptylopora. The fragment named Retepora pluma by 
Phillips, must not be confounded with Ptylopora pluma McCoy. I 
have a specimen of the latter species from Malahide, and the species 
is very well figured in Nicholson s Manual of Paleontology^ Vol. L, 
p. 423. Sometimes the fossil here described is present in the 
Limestone as casts only, it is then seen that the place in the zoarium 
which the central stem occupied is a long and central furrow, and 
the surrounding cast has some resemblance to a minute auger, and 
when seen for the first time, is likely to be a complete puzzle to the 
palaeontologist. As the genus is a rare one, these minute particulars 
may be the means of drawing the attention of the student to special 
features, such as the apex and the base, which are not so well 
known. 
6. Ptylopora pluma? McCoy. (Compare with Figs. 2G3, p. 422, Manual 
of PalcEontology, Nidi. yoI I., with Fig. 9, p. 14, Pages Introductory Text Booh 
of Geology). 
I am not certain that this is really the P. jiluma of McCoy, as the 
only portions of the Zoarium that I have are the central stem with 
some of the lateral branches. Accepting Nicholson's fig. as above 
I will now describe the fragments. Central stem (Glauconome 
like), the origin of the stem appears as a root-like prolongation 
divided into narrow prongs altogether unlike the stem in its after 
development ; higher up rootlets appear on the sides, and higher 
still the normal character with lateral oblique fenestrations as in 
ordinary Ptylopora. Normal stem with a broad central rounded 
keel bearing in the sides a row of cells, alternately placed on either 
side of the keel — keel spinulose along the centre. Branches united 
by dissepiments which are rather broad in the junction ; apparently 
destitute of keel. Fenestrules rather broad, slightly oval bearing 
on either side three cells, — openings circular. General shape and 
size of Zoarium unknown. 
Locality. — Castlelon, Derbyshire. 
There is a marked difference between this and P, Phillipsia. 
