ON FOSSIL POLYZOA. 169 
The type H. frondiculata, Lamx., is a well-marked species, and is 
admirably described and figured by Mr. Busk in Pt. iii. (Cyclostomata), 
‘Brit. Mus. Cat.’ p. 17, Pl. xx. figs. 1, 2,3, 4. The genus is doubtfully 
represented in the Cretaceous epoch; but as the Siphodictyum of Lonsdale 
very closely resembles some of the admitted Hornera of Miocene age 
in continental catalogues, it may be well to admit it in ours also. _Hagenow 
admits one species, H. tubulifera, Hag. 
Horner? GRACILE, Lonsdale. 
=Siphodictyum gracile (Lower Greensand, ‘School of Mines Catalogue’). 
Family V. Licnenoporipz, Smitt. 
Genus Licurnorora, Defrance. 
‘Zoarium discoid, raised, simple, or composed of many confluent 
disks, entirely adnate, or partially free, and sometimes stipitate, developed 
on a thin lamina which usually forms a border round it. Zowcia distinct 
or connate, in single radiating lines, or multiserial.-—‘ Brit. Mar. Polyzoa,’ 
. 471-2. 
te This genus willinclude the following genera of D’Orbigny, but species 
are not abundant in our British Cretaceous rocks. 
a. Confluent disks: Radiopora, Unicavea (sp.), Discocavea (sp.). 
f. Adnate with multiserial rays: Actinopora, Discotubigera. Mr. 
Hincks says: ‘The genus is widely distributed both in space and time ; 
in the Cretaceous beds it is represented by a large number of beautiful 
forms.’ 
‘D’Orbigny has constructed a large number of genera, which are 
merely arbitrary groups based on very trivial modifications of this well- 
marked type.’ 
Genus Rapropora, D’Orb. 
‘Zoarium adnate, crustaceous, spreading irregularly, and composed 
of confluent disks like those of Discoporella; surface reticulate or can- 
cellous ; cells disposed in serial lines, radiating from the centres of the 
constituent disks.'—Busk, ‘ Cyclostomata,’ p. 34. 
In the Lower Greensand and also in the Chalk we have species that 
are and may be referred tothis genus. In Prof. Morris’s, Cat. Brit. Foss.’ 
two species are named—R. pustulosa, D’Orb., and R. millepora, D’Orb.— 
both of which are before me, but there is a great difference in the two 
types. A species from the Chalk (Freshwater Bay, Isle of Wight) very 
closely resembles one of the figures of Ceriopora diadema, Goldfuss. 
In retaining the genus Radiopora Mr. Busk remarks : ‘ In the majority 
of the fossil species referred by M. D’Orbigny to this genus, the zoaria are 
more or less rounded or bulbous, owing to the superposition of layer upon- 
layer of the confluent disks; but in one, R. Francquana (1, c. p. 997, pl. 782, 
figs. 3-8 ‘Pal. Franc.’) this superposition would seem to have taken 
place only to a very slight extent. In the two living forms I have re- 
ferred to the same genus there is no superposition at all; butas the mode 
of growth is in other respects so exactly in accord with M. d’Orbigny’s 
excellent description, I have not thought it expedient to institute another 
genus, or even subgenus, merely on that account.’ 
Mr. Hincks (‘ Brit. Mar. Polyzoa,’ p. 473) does not make a separate 
