G. K. VINE ON THE WENLOCK POLYZOA.
Pies. 11-13. — Ptilodictva Lonsdalei, Vine.
m
11. Section nearly parallel to the central axis, showing the marginal cells, and
tbe compressed perpendicular cell

X 20.
12. A portion of the same, further enlarged

X 40.
13. A portion of the non-poriferous margin of another section

X 40.
Localities. Though rare in some of the washings, more or less
abundant in all the shales below the Wenlock Limestone. Very
rare, though I have found a few fragments, in the shales No. 46
over the Wenlock Limestone.
Affinities. This species resembles to some extent P.flagellum, Nich.
(Ann. & Mag. Nat. Hist. March 1875, pi. xiv. figs. 3, 3 6 ), except in the
fiexuous character of .the base. There is a slight difference in the
measurements of the two species

and Nicholson does not allude to
any distal openings, while these are a marked feature in P. Lonsdalei.
I have not specimens for comparison

but I have not the least doubt
that it will be found that the Llandovery and Wenlock P. lanceo-
lata may be placed here. My only objection to describing the frag-
ments as typical of Lonsdale's species is that the Wenlock Limestone
type is altogether different and considerably larger. Under these
circumstances 1 dedicate the species to Lonsdale's memory.
In the description of this type I have indicated the function of
the " non-poriferous margins " of Ptilodictya by speaking of them
as the "endocystal layers." Taking the endocyst and the ectocyst
together, the latter being only a structureless excretion from the
endocyst charged with a protective function

• ,

it may be well to direct
attention to this physiological feature. I have ascertained that the
enlargement of the colony of Ptilodictya takes place at the distal
openings and also at the margins. After a time enlargement at the
distal openings becomes abortive, and these indications of a function
remain as ornaments only. It is different on the margins

here
life is more active, and enlargements take place on the younger por-

Hincks's Brit. Mar. Polyzoa, p. x.
Q.J.G.S. No. 149.