56 A MONOGRAPH OP THE TERTIARY POLYZOA OP VICTORIA. 



permanently open, or become closed throughout the whole extent, their situation 

 being still marked by a suture or groove, or they may be closed at intervals by 

 calcareous cross-bars or trabeculse leaving regular series of openings or pores. 



Membraniporella, Smitf. 



Zoarium encrusting or foliaceous. Zooecia contiguous or disjunct ; closed in 

 front by a series of more or less consolidated calcareous ribs. 



1. M. distans, McG. 



Membraniporella distans, McG., P.Z.Y., 187. 



Two single damaged zooecia from Muddy Creek belong either to M. distans or 

 the well-known closely allied European M. nitida. The specimens are not sufficient, 

 especially in the absence of ooecia, for satisfactory identification, but as 31. nitida 

 has not, so far as I know, been found living in Australia, I refer them to the recent 

 Victorian species. 



2. M. tenuicosta, n.sp, PI. VIII., figs. 15, 16. 



Zooecia ovate, distinct, separated by narrow grooves ; outer part of anterior 

 surface smooth, middle part raised and formed by a series of 8-16 narrow ribs on 

 each side ending in a narrow central ridge, the intervening fissures remaining open 

 or partly or wholly filled in by a thin calcareous extension from the ribs ; thyrostome 

 large, wider and slightly arched above, lower lip slightly hollowed and with a 

 prominent denticle on each side ; thyrostome of ovicelligerous cells wide, nearly 

 semicircular, the lower lip straight or very slightly hollowed and without denticles. 

 Ooecia large, prominent, rounded, a vertical raised rib with a depression on each 

 side extending nearly the whole length. 



S.P.; M.C. 



The furrows between the ribs are in most of the zooecia filled in by a thin 

 calcareous membrane along the centre of which is a partial or complete slit-like 

 fissure which is frequently closed, its situation being then usually indicated by a 

 faint line. This species differs from the others of the genus in the exceeding 

 narrowness of the ribs and the more complete denticulate thyrostome. Except for 

 the absence of the trabeculae between the ribs and their great tenuity, it bears a 

 considerable resemblance to Cribrilina orbicula. I am not quite satisfied that it 

 ought not to be referred to Cribrilina, as I have an imperfect specimen, which 

 may belong to the same species, in which the margin, although narrower, is smooth, 

 the front a little broader, the ribs thicker and joined by regular small trabeculae and 

 the thyrostome of nearly the same structure but not so widened above. At the 



