28 
Remai'ks on the Eleidae and the Ceidae. In a paper: „On 
Chilostomatous characters in Melicertitidae and otlier fossil Bry- 
ozoa“ Waters^) bas shown tbat some structures occurring in tbis 
division of exstinct Bryozoa, wbicb have earlier been described as 
ooecia, are really avicularia, and he is iuclined to suppose that 
tbese Bryozoa have also been provided witb an operculum, but of 
tbis be bas not been able to convince bimself. The division Elei¬ 
dae (—Melicertitidae) was founded by d’Or bi gny-) wbo in oppo¬ 
sition to all the later authors regarded the calcareous plate in 
many species closing the orifice of more or less zooecia, as a real 
operculum. It is a well known faet that the orifice of old zooecia 
in many species botb of Cijclostomata and of Cheilostomata is closed 
by a calcareous plate, no doubt for the purpose of protecting the 
elder zooecia deprived of tbeir polypide, tberefore the whole colony 
from destruction, and the named calcareous plate is at present re¬ 
garded as a similar closure. In many species of Eleidae we eau 
find the orifices closed in two different ways, namely in some zooe¬ 
cia by a convex calcareous plate witb distinet, free margins and 
fiabelliform striation, and in others by a coneave not striated plate 
continuous with the inner surface of the zooecium. In most cases 
the superior part of this plate is provided with a projection, per- 
forated by an opening, and very similar closures provided with a 
projecting tube have been found in a number of Cyclostomata and 
even in some Cheilostomata^). In other species we can only 
find orifices closed in the last named manner. While there can 
be no doubt that the coneave plate is a closure of the same 
kind as that found in many Cyclostomata and Cheilostomata, the 
convex striated plate must be regarded as a true, calcareous oper¬ 
culum and in such species in which it has not been found we 
Annals nat. hist. S. 6, Vol. VIII, pag. 48.. 
2) Op. cit. pag. 606. 
3) Waters, North-Italian Bryozoa, Qiiart, Journ. Geol. Soc. 1891, Vol. 
XLVII, PI. III, fig. 4. 
