334 SIDNEY F. HARMEE. 



acquire great importance in throwing light on the structure 

 of some of the Escharine forms. If a given species has a 

 Cribrilinid ancestry, it might be expected that the roof of the 

 compensation-sac would be formed by the deeper surface of 

 the frontal shield (figs. 12, 50). If, on the contrary, the 

 frontal shield is a cryptocj'^st, it might be anticipated that the 

 compensation- sac would have a membranous roof distinct 

 from the frontal shield. Although this arrangement is indi- 

 cated in fig. 34 (Euthy ris obtecta) I cannot assert positively 

 that it is the case in that species. There is, however, no 

 doubt of the existence of a complete membranous roof to the 

 compensation-sac in Euthyris clathrata (figs. 26, 27). 



There are other considerations which indicate that the 

 frontal shield may, in certain Escharina, be a cryptocyst. 

 Numerous Membraniporidte, both recent and fossil, show a 

 tendency to develop a cryptocyst, although in many cases 

 complete proof that the calcified '' area " is of this nature is 

 not yet forthcoming. The case of Bicellaria grandis 

 (fig. 1) is again uncertain. But the fact which is, perhaps, 

 most significant is that in certain species of Schizoporelia 

 (fig. G), Microporella, etc., the region encircled by tlie 

 marginal spines of the primary zocecium is partially calcified 

 proximally. It appears to me to be of great importance to 

 ascertain whether this calcified portion is of the nature of a 

 cryptocyst oi' not ; — in othei- words, whether the frontal 

 membrane extends as far as the sharp ridge on the inner 

 side of the base of the spines. I can hardly doubt that this 

 is the case ; and if so, the Mici'oporoid origin of Escharine 

 forms in which the compensation-sac develops as an invagi- 

 nation at the base of the operculum would appear to bo 

 indicated. The Cribrili na-like character^ of certain species 

 of Catenicella, in which the sac develops in this way, is, 

 however, a difficulty which requires further explanation. 



' Tliis character is indicated in fig. S.") of llie present paper, and in many 

 figures on pis. i and ii of MacGillivraj's "Monograph of the Tertiary Polyzoa 

 of Victoria" ('Trans. Roy. Soc. Vict.,' iv, 1895). Tiie Escliarine nature of 

 the Cateniceliida; is noticed l)y Sniitt (ISOS, 2, p. 40). 



