IDilOXEA. 
153 
side view are seen to occur in regular transverse series. Zoarium 
with ribbed selvage ; x 8 dia. ^ddle Chalk : Chatham. Gamble 
CoU. D. 465. 
PI. YIII. Pig. 3. A zoarinm with more regular, subclavate 
zoarial ridge and smooth selvage (the elevations on the latter are 
due to the granules of the echinid plate which the zoarium is 
encmsting) ; X 7 dia. Middle Chalk : Chatham. Gamble Coll. 
D. 3843. 
Affinities. 
This Biyozoan is most nearly allied to Idmonea hagenowi 
(Sharpe), from which it differs by the great width of the selvage 
and the simple form of the zoarium. The central ridge in its 
proximal end resembles Prohoscina anomala, Eeuss, but that species 
has neither the regularly alternate peristomial rows nor the broad 
selvage of Idmonea alipes. A resemblance to P. anomala may also 
he recognized in some specimens when examined from above, as 
in PI. VIII. Pig. 2 ; but on a lateral view the regular transverse 
rows of peristomes show that it is a true Idmonea, and has no 
connection with P. anomala. 
LIST OP SPECIMEiS^S. 
D. 465. A long, somewhat irregular zoarium, with pinnately striated selvage 
and the apertures in transverse series of Irom two to four. On 
a fragment of Inoceramus. Middle Chalk ; Chatham. Gamble 
Coll. Figd. PI. VI 11. Fig. 2. 
D. 8843. A typical zoarium on a fragment of Mxcraster. Middle Chalk. 
Chatham. Gamble Coll. Figd PI. VIII. Fig. 3. 
D. 983. A zoarium on an echinid fragment (on slide). Middle Chalk. 
Chatham. Vine Coll. 
D. 4106. A zoarium on a hinge of Inoceramus. Middle Chalk. Chatham. 
Gamble Coll. 
D. 3976. A double zoarium, two branches rising from a common centre ; on 
a fragment of a Micr aster (on slide). Middle Chalk. Chatham. 
Gamble Coll. 
D. 3841, D. 3842. Two zoaria on fragments of Micraster (on slides). Middle 
Chalk. Chatham. Gamble Coll. 
? D. 3876. A broken specimen (on slide). Middle Chalk. Chatham. Gamble 
Coll. 
? D. 4368. A clavate zoarium (on sUde). Middle Chalk. Chatham. Gamble 
CoU. 
