90 Canon A. M. Norman—WNotes on the 
(? rosette-plates), the appearance of which was exactly that 
of those figured as characteristic of the genus Steganopora 
(see d’Orbigny, Paléont. Franc., Terr. Crét. pl. decxxi. figs. 3, 
7,11; and Jullien, ‘‘ Les Costulides,” Bull. Soc. Zool. de 
France, 1886, pl. xvii. fig. 2 and pl. xix. fig. 2). 
The Zoecium-building in Cribrilinide. 
In describing the structure of Lepralia (Membraniporella) 
nitida, Hincks wrote that “in its earlier condition it closely 
resembles one of the spiniferous Membranipore. ‘The ribs of 
the adult state are represented by suberect spines set round 
the margin. As growth proceeds the spines bend inwards 
and increase in size, and gradually take on the flattened rib- 
like appearance. After a time the opposite rows meet in the 
centre of the cell-area, and the extremities, which are often 
enlarged, are soldered together, so as to form a well-marked 
median line. In some instances the ribs unite laterally to a 
great extent, and the front becomes a solid wall. In others 
they continue quite separate.” In his account of Cribrilina 
annulata he writes:—“In its earliest stage the zocecium 
exhibits the simple Membraniporidan form—the area occu- 
pying the entire front and being closed by a membranous 
covering. The ribs which compose the frontal wall in the 
adult are given off on each side as tubular processes from the 
edge of the nascent.cell, and, gradually lengthening, meet in 
the centre and unite, the line of junction giving the subcarinate 
appearance of the zoccium. These tubular girders, which 
are probably the equivalent of the marginal spines on many 
of the Membranipore, are connected at intervals by lateral 
outgrowths of calcareous matter; and in this way the porous 
structure of the furrows is produced. The mode of formation 
may be well studied in the thickened anterior margin of the 
orifice, which is composed of two tubular pieces, the pointed 
extremities of which in meeting often bend outwards and 
give rise to the central mucro. Sometimes they are not 
closely welded together, but overlap one another or remain 
partially separate, so as to give a bifid appearance to the 
mucro. Occasionally they do not unite at all, but continue 
permanently free and detached.” 
All this is im every particular correct as regards the 
two species referred to; and the description of Cribrilina 
annulata, of course, was intended to be applicable in a general 
sense to the whole of the species which he placed in Gray’s 
genus Cribrilina. My object in the following notes is to 
go intothe question more minutely, for the purpose of showing 
