ME. A. W. WATEES OJST MEMBEANIPOEIDiE. 655 



been studied by Nitscbe*, Freesef, VigeliusJ, andProulio§, 

 but this has been confined to the Memhranipora pilosa and 

 meiribranacea groups, and it is very desirable that some of the 

 other sections should be thoroughly examined. In the M. pilosa 

 the intertentacular organ is known, and the larva occurs as 

 Cyphonautes : thus in both particulars correspondiog with Alcyo- 

 nidium and some Ctenostomata, but in the other groups we 

 know nothing of the anatomy. 



The recent Membraniporidse ai-e mostly incrusting, but this is 

 not always the case, as may be seen in M. Jiians, Hincks ; 

 M. perfragilis, H. ; M. tuhigera, B. The first two are sometimes 

 unilaminate, sometimes bilamioate, and in fossils bilaminate 

 forms are fairly abundant. The M. sigillata of Pourtales is 

 reticulate. The margins are raised ; there is a membrane over 

 the front of the zooecium, and in this the operculum, which is 

 " incomplete," is situated. In some species the ova are developed 

 without ovicells ; in others the ovieell is immersed or prominent. 

 The avicularium only exceptionally has a complete bar. 



The most important character is the operculum attached to 

 the membranous cover ; and the first impression that they were 

 in this family too similar to furnish useful characters has been 

 entirely modified, and it is seen that in forming groups they 

 must not be neglected, and in fact the examination ot this organ 

 shows that one group must be removed on this account to 

 another genus, and perhaps should go to another i'amily. 



This group was indicated by Jullien || under the name 

 Ghaperia ; but while he based it upon two lateral plates, which 

 I have shown are for the attachment of the opercular muscles 

 and do not occur in all species, the important character is the 

 form of the operculum, which is separable, and which has at each 

 side an elongate protuberance ibr the attachment of the muscles 

 (PL 47. figs. 9, 10). This group, which was no doubt abundant 



* " Beitrage zur Kenntniss der Bryozoeu," Zeit. f. wissensch. ZooL 

 Tjl. xxi. 



t " Anat.-hist. Untersuch. von Membranipora filosa," Arch, fur Naturgesch. 

 vol. i., 1888. 



I Die " Bryozoen " gesammelt wahrend der dritt. u. viert. Polarfalirt des 

 Willem Barents. 



§ "Contrib. a I'histoire des Bryozoaires," Arch, de Zool. Exp. ser. 2, vol. s. 

 p. 557. 



I| " Eemarques sur quelques Especes de Bry. Cheil.," Bull. Soc. Zool. de 

 France, vol. vi. 



