A MONOGRAPH OP THE TERTIARY POLTZOA OP VICTORIA. 57 



same time I have a single zocecium, which is undoubtedly M. tenuicosta, in which 

 the ribs are much more highly calcified and thicker and separated by distinct 

 fissures throughout their whole length. 



Cribrilina, Gray. 



Front of zooecia formed by the partial coalescence of marginal spines or ribs, 

 the intervening spaces depressed and occupied by a series of pores or perforations, 

 or more completely filled in so that the prominence of the ribs disappears, and the 

 front is occupied by radiating or concentric series of pores. 



Cribrilina differs from Membraniporella in having the ribs united by cross 

 growths of calcareous matter, leaving numerous j>ores. The genus ought to be 

 restricted to those species in which the pores, from being arranged in regular 

 radiating or concentric series, show that they are formed by the partial junction of 

 the transverse ribs. Species in which the anterior pores are simply spaces left in a 

 general calcareous ingrowth from the margins of the zooecia ought clearly to be 

 referred to genera of other families. 



1. C. orbicula, n.sp. PI. VIII., fig. 17. 



Zooecia wide, somewhat hexagonal, distinct ; outer part smooth, the middle 

 slightly raised, rounded, closed by about eighteen narrow ribs on each side, the 

 intervening furrows crossed by small trabecule leaving regular concentric series of 

 minute linear pores ; thyrostome wide, arched above, slightly narrowed below and 

 with an obscure denticle at each angle. 



M.C. 



This very beautiful species is at once distinguished by the broad, smooth 

 margin of the zooecia, the number of the narrow costae and the regular concentric 

 linear pores in the intervening furrows. 



2. C. suggerens, Waters. PL VIII. , fig. 8. 

 Cribrilina suggerens, Waters, Q.J.G.S., 1881, p. 327. 



Zoarium very small, rarely encrusting, almost always bilaminate. Zooecia 

 ovate, raised, flat or depressed towards the centre ; about six or eight rows of short, 

 nearly vertical, open tubes on slightly raised ridges, diverging on each side from the 

 median line, and arranged so as to form also concentric series. In the furrows 

 between the rows of tubes numerous distinct round pores alternating with the 

 tubes ; thyrostome small, semicircular. 



S.P. ; M.C. ; B. ; C.C. (W.) 



