ELEID^. 
287 
c'vliiidrical, and exclude the adnate forms. The Melicertitiiia of 
Pergens is unsatisfactory, as the diagnosis states that there are no 
external ‘ovicells,’ and the structures which, as we shall see, are 
no doubt a^ucularia, were described as ovicells. There seems no 
reason why d’Orbigny’s well-founded family, the Eleidoe, should he 
<lisplaced by cither of the groups subsequently proposed. 
Eleid Chae.vcters and Cyclostomatous Avictilaeia. 
In the various diagnoses of Busk’s orders, the Cheilostomata and 
Cyclostomata, stress is usually laid on two characters : ^ ( 1 ) that 
in the Cheilostomata the apertures are subterminal, operculate, 
und rarely circular, whereas in the Cyclostomata the apertures 
iire terminal, inoperculate, and usually circular; (2) that in the 
Cyclostomata there are no avicularia or vihracula. 
The Cretaceous family, the Elcidae, is important, as it breaks 
down the distinction between the Cheilostomata and Cyclostomata, 
based on these characters. D’Orhigny founded this family in 1853 
for a series of Bryozoa with anomalous characters, of which the 
most striking was the presence of a series of modified zooecia that 
he described as ‘ cellules accessoires.’ These accessory structures 
iirc of two types, large superficial marsupial chambers, and cells 
with triangular or elongated apertures and a platform parallel to 
the surface of the zoarium. The marsupial chambers were 
described by d’Orhigny as ‘cellules ovariennes,’ and they arc 
clearly gonocysts or gonoecia. The nature of the second set is 
more important. D’Orbigny recognized that they sometimes occur 
on the same specimen as ‘cellules ovariennes,’ and therefore 
cannot be ovarian. He suggested that they may he male cells or 
sperm - cells.^ Nevertheless, Pergens and Marsson subsequently 
described them as ovicells. Canu, recognizing that this view is 
a mistake, has proj)osed for these structures the name ‘ eleo- 
ccllaires.’ AVaters, however, has maintained that they are 
avicularia, and his reasons are convincing. “ The presence of 
^ Thus Busk’s latest definition of the Cyclostomata (Eep. Chall. Exped., 
ZooL, vol. xvii. 1886, p. 1) is “ Zooecia tubular, calcareous, partially free or 
wholly connate or immersed ; aperture terminal, inoperculate.” Hinck’s 
diagnosis (Brit. Mar. Polyz., 1880, p. cxxxix) adds the second character : 
“ Zooecia tubular, with a plain, inoperculate orifice. Marsupia and appendicular 
organs [avicularia and vihracula, v. p. cxxxvi] wanting.” 
^ D’Orbigny ; Bry. Cret. p. 99. 
