ELEID.E. 
289 
Unplooecia differs from the normal Entalopliorids only by the 
constriction of the aperture, wliicli is subterminal instead of 
terminal in position. It has no avicularia, and its zooecia are 
monomoi’pbic. 
The next stage in the evolution of the Eleidae is represented 
by a Bryozoan from the Lower Greensand beds of the Isle of 
AYight, which was desciibed by Lonsdale as Chisma fur cilia him. 
The normal zooecia in this species agree with those of Haplooecia 
{cf. figures of Lonsdale’s type on PI. XI. Eigs. 14, 15) ; but in 
addition to them there are some elongated zooecia of a different 
type. The specimens arc not well preserved, so the character of 
the zooecia with these elongated apertures is open to some doubt. 
But they are probably a simple form of the type of avicularium 
present in Meliceritites lonsdalei, in which the aperture is circular 
or elliptical, below a depressed area bounded by the distal pro- 
longation of the peristome. The avicularium has been formed 
by the development of a platform above the aperture, which is 
itself of the nonnal form. The close resemblance of Meliceritites 
lonsdalei to the Entalophoridte is shown by the fact that the species 
has hitherto been included in the genus Fustulopora. 
A more specialized form of avicularium occurs in some species 
such as Meliceritites undata (PL XVI. Eig. 3), in which the broad 
platform for the support of the mandible is notched by the upper 
end of the triangular or trigonal aperture. 
Hence there is known a fairly complete series of stages in the 
development of these avicularia from normal Cyclostomatous 
tubular zooecia. 
The other characters usually regarded as typical of the Cheilo- 
stomata also occur in the Eleidae ; for the aperture is smaller 
than the diameter of the zooecia, and is lateral or subterminal. 
The presence of an operculum cannot be positively asserted, 
but its occurrence in the Cretaceous Eleidae is probable from 
e^fidence cited by Waters, who has described in his Meliceritites 
roijana a contraction formed by a curved plate below the aperture ; 
he remarks that “possibly an operculum has an attachment here, 
but of this I have not been able to satisfy myself.” As the 
opercula are chitinous, it is not to be expected that they should 
be found fossil, and only indirect evidence of their presence, such 
as traces of their attachment, is probable. 
The presence of opercula in Cyclostomata has, however, been 
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