DESCRIPTION OF CHALK CORALS. 273 
The young circular crusts had no apparent fixed points of development, some- 
times coinciding in position with the centre of the subjacent disk, but sometimes 
were nearer the edge. If rightly understood, the earliest observed state presented 
a few confused vertical cavities of limited extent (fig. 2a@-+); while a little more 
advanced condition gave a disk-like form, with nearly horizontal, radiating tubes. 
The assumed earliest patches were not however always limited to so smal! an area 
as in the case delineated (fig. 2 a t), occasionally covering a relatively consider- 
able space, as if the reproductive power had been more diffused. There was no 
distinct base lamina, like that which occurs in Tubulipore ; but in the immediate 
vicinity of the somewhat advanced disks, the old tubes of the subjacent layer 
had for the greater part closed mouths, and the general surface was thickened, 
as if a preparatory inseparable foundation had been laid for the future construc- 
tion. From this subsurface projected, moreover, the sides of the tubes in progress 
of formation or laid open by fracture. 
(Tab. XVIII. fig. 35* ; and XVIII. A. figs. 3, 3 a.) 
Attached throughout, branched ; branches bifurcated with intermediate fan- 
shaped areas of limited growth; tubes minute, produced either at the termina- 
tion of the preceding or intermediately ; mouths simple, tubular extremities. 
The above characters must be considered rather as those of the specimen exa- 
Diastopora 
mined, than of a species. In the branched mode of growth, a resemblance will 
be found in M. Michelin’s Diast. ramosa' which is also a cretaceous zoophyte ; 
but if the English fossil exhibits a normal and not an accidental manner of de- 
velopment, a distinction exists in the points where the bifurcations commence 
not ceasing at once to be productive, but giving forth in two cases additional 
tubes which assumed a fan-shaped area: they had possessed, however, apparently 
a limited amount of vitality in comparison with the adjacent branches, and 
some of their tubes had not been provided with distinct apertures. Another 
difference from Diast. ramosa is the minuteness of the coral. A branch of M. 
Michelin’s species, half a line in width, exhibited transversely only three to four 
apertures, as shown in his enlarged figure, 3 b, whereas a space of equal breadth 
in the English fossil gave at least eight. 
The species to the extent displayed (figs. 3 & 3 a) would belong to M. Edwards’s 
first division of the genus, or to that composed of Diastopore, which form a 
single layer. In having a branched plan of growth, a certain amount of resem- 
' Teon. Zoophy. p. 203. pl. 52. fig. 3. 
