ON FOSSIL POLYZOA. 197 
family Prizcpicrronipa, Zittel emend. Ulrich ; the second is STICTOPORIDH, 
Ulrich. 
In the first of these families Mr. Ulrich places the following genera :— 
1. Péilodictya, Lonsdale. 3. Arthropora, Ulrich. 
2. Graptodictya, Ulrich. 4, Dicranopora, ,, 
5. Clathropora, Hall. 
As Ptilodictya, Lonsdale, is taken as the type of this family, I shall 
make no apology for working out the structural characters of one, at 
least, of the forms upon which Lonsdale founded his genus. 
1839. Prizoprctya, noy. gen. (Lonsd.). 
Derivation—zritoy pluma, cixtvoyr rete. 
‘Thin elongated expansions, having on each surface small quad- 
rangular cells, not convex, which penetrate the coral obliquely, and are 
arranged, with respect to the surface, along the middle of the specimen, 
parallel to the elongated direction of the coral, but in the sides obliquely 
from it. Surface a very thin calcareous crust, traversed by slightly 
raised ridges, marking the boundary of the cells; towards the margins 
the crust thickens ; the indications of the cells are less distinct, and at 
the edges are invisible, but cells are traceable close to the margin where 
the crust has been removed; opening of the cells small, transversely 
oval? No indication of a central partition parallel to the surface.’— 
* Silurian Syst.’ p. 675, pl. XV. 
Ptilodictya lanceolata, Lonsd. p. 675, fig. 11 to 11 c. 
‘Small fragments of probably young specimens of this species are 
occasionally found in the slabs of Wenlock Limestone. One of them is 
represented in pl. XV., fig. 11 b, 11 c.’-—Lonsdale. 
Pritopictrya Lonspauet, Vine. 
Notes on the Polyzoa of the Wenlock Shales, &c., ‘ Quart. Jour. Geo. 
Soe.’ Feb. 1882; Second Brit. Assoc. Report on Foss. Polyzoa, mihi, 1881, 
for information on the genus generally. 
I have already described, under the name Piilodictya Lonsdalet, 
some of the ‘ young specimens’ referred to by Lonsdale. In that descrip- 
tion I spoke of certain peculiar structures in the species (p. 66) with a 
promise that ‘I should return to their discussion at some future time 
when other investigations were completed.’ I now redeem the promise, 
in the hope that other Paleontologists will examine the species in their 
own localities, and compare them with these type specimens of Lonsdale. 
I. Superficial characters of Ptilodictya Lonsdalei, Vine. If we take 
a number of the fragments of this species, which we shall find rather 
abundantly distributed in the Wenlock Shales, and submit them to a 
tolerable heat in the fire, plunging them immediately after into water, we 
shall soon getrid of the ‘crust,’ and some peculiar structures will be revealed. 
The ‘small quadrangular cells’ referred to by Lonsdale will be seen to 
perfection, and according as the preservation of the zoariwm is cal- 
careous or ferruginous, the walls will be either of a white or of a dark 
brown colour. The rows of cells in a longitudinal direction are separated 
by dividing ridges, or by slightly raised ridges also referred to by 
