28 
Remarks on the Eleidae and the Ceidae. In a paper: ,,0n 
Chilostomatous characters in Melicertitidae and other fossil Bry- 
ozoa" Waters!) has shown that some struetures occurring in this 
division of exstinct Bryozoa, which have earlier been described as 
o0ecia, are really avicularia, and he is inclined to suppose that 
these Bryozoa have also been provided with an operculum, but of 
this he has not been able to convince himself. The division Elei- 
dae (== Melicertitidae) was founded by d'Orbigny?) who 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 fact that the orifice of old zooecia 
in many species both of Cycløsiomata and of Cheilostomata is closed 
by a calcareous plate, no doubt for the purpose of protecting the 
elder zooecia deprived of their polypide, therefore 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 can 
find the orifices closed in two different ways, namely in some z00e- 
cia by a convex calcareous plate "with distinct, free margins and 
flabelliform striation, and in others by a concave 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 CAeilostomata?). In other species we can only 
find orifices closed in the last named manner. While there can 
be no doubt that the concave 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 
1) Annals nat. hist. S. 6, Vol. VIII, pag. 48. 
2) Op. cit. pag. 606. 
”) Waters, North-Italian Bryozoa, Quart. Journ. Geol. Soc. 1891, Vol. 
XLVIL PL BI, fig. 4, 
