EETECATA. 
191 
Diagnosis. 
Zoarium of thick, frequently dichotomizing branches, rising from 
a thin, expanded base. The branches are all approximately 
in one plane. The branches are laterally compressed at the 
distal ends, and they are marked by a median keel or ridge ; 
hut in older parts of the branches the two rows of zooecia 
are separated by a gi’oove. Eeverse surface well rounded, 
with small interzooecial depressions. 
Peristome of the innermost zooecium of each series is well raised 
and prominent; and the distal ends of the branches, when 
viewed fi’om the obverse side, may appear imiporous. Yiewed 
laterally they are seen to he hiserial or triserial, and in the 
proximal parts of the zoarium each series consists of four or 
five apertures. 
The transverse series are vertical. 
Distribution. 
England : 
Upper Chalk: Sussex; Portsmouth; Bromley; Yorthfleet. 
Foreign : 
Senonian — Maastrichtian : Meudon; St. Germain; Sainte-Colombe, 
Mauche ; Chateaudun, Eure-et-Loir ; Ciply ; Royan. 
Campanian : Riigen ; Quarnby, Sweden. 
Santonian : Saiiites, Perignac, Pons, etc., Charente- 
Inferieure ; Arche de Leves ; Cachembach. 
Coniacian : Yenddme, Les Roches, Villedieu, and Lisle, 
Loir-et-Cher ; Tours, Indre-et-Loire. 
Turonian: Merpins, Chareute. 
Figures. 
PI. IX. Fig. 8. Parts of three of the specimens figured by 
Lonsdale. Fig. obA^erse side of the end of a branch, showing 
the prominent median keel ; X 8 dia. Fig. 8J, part of a lower 
branch, in which there is a median furrow instead of ridge ; 
X 8 dia. Fig. 8^?, part of a branch, from the side ; X 8 dia. 
Upper Chalk : Sussex. Dixon Coll. D. 2955. 
Affinities. 
On casual inspection of the specimens which Lonsdale figured 
as I. cretacea, they appear to differ from Milne Edwards’ 
species. For in some of Lonsdale’s fragments there is a definite 
raised median line along the obverse face of the branches, and the 
