290 
ELEID.^:. 
affirmed owing to tlie closure of some zooeeia by a thin pellicle. 
Zooecia are thus closed both in Cheilostomata and Cyclostomata ; 
and the occurrence of these calcareous films above the position 
of the operculum in Cheilostomata^ shows that they cannot be 
regarded as opercula. The nature of these closures is uncertain. 
They occur in zooecia scattered all over the colon}’, and amongst 
open zooecia ; hence they are not due to an epithecal growth 
over the basal, dead zooecia of a zoarium. It is also improbable 
that the closure is a seasonal protection, like the epiphragms that 
cover the mouths of snail shells during the winter; for Chalk 
bryozoa with such closed zooecia must have lived in a moderately 
deep sea, below the limit of seasonal change. Similarly closed 
cells, which are sometimes covered by an inverted funnel-shaped 
cap pierced by a pore, are known among recent Cyclostomata. 
Smitt suggested that such zooecia were sperm cells, and Hincks 
quoted the hypothesis as plausible. Some of the Chalk Brj’ozoa 
{e.g. PI. XIV. Pig. 4) have the same type of closure, consisting 
of a conical cap pierced by a pore. 
Another possibility in regard to these closed cells is that they 
are zooecia in process of regeneration by the degeneration of the 
polype into a ‘ brown body, ’ from which a new polypide is 
formed. This regeneration of zooecia is well known among 
Bryozoa, and it offers the most satisfactory explanation of these 
closed cells. 
As, then, the Eleidoe have a lateral aperture, avicidaria, external 
gonoecia or gonocysts, and probably, in some cases, also a true 
operculum, the only point in which they agree with the diagnosis 
of the Cyclostomata given by Busk and Hincks is that the zooecia 
are tubular. But this character clearly shows the CycloStomatous 
origin of the Eleidoe, which appear to have developed through the 
Haplomia- Chisma series from the Entalophoridae. 
Whether the Eleidae became extinct in the Cretaceous, and 
whether they left descendants, is doubtful. It is possible that, 
by continued reduction of the proximal end of the zooecium, 
the Eleidae gave origin to some members of the Stolonata or 
Cellularina. 
^ E.g. in Porina coronata (Rss.), Waters. V. Ital. Bry. : Quart. Jouru. 
Qeol. Soc. vol. xlvii. 1891, p. 25, pi. iv. figs. 2, 15. 
