256 DESCRIPTION OF CHALK CORALS. 
to it, even in the very youngest parts of the coral; the number of tentacula is 
eight ; the branches or lateral segments issue, with rare exceptions, from the cal- 
careous portions of the main stems ; and as the coral advances in age, the intervals 
are overlaid by a layer, similar in composition to the substance of the segments, 
the lower part of an old specimen, presenting a continuous or uniform cha- 
racter’. 
Scilla’s figure of Isis Melitensis was drawn from detached portions found near 
each other and put together (op. cit. p. 63). The coral however agrees with 
Isis Hippuris and other recent species in the general form and furrowed exterior, 
when perfect, of the segments ; but it differed in their terminations having con- 
vex or concave articular surfaces with a central foramen; and the ligament, 
whatever may have been its nature, had apparently far less thickness than in Js. 
Hippuris ; whereas in the recent coral there are no articular surfaces, the ample 
horny intervals affording great facilities for motion. So far as the fossil is de- 
scribed or figured in the works consulted, or specimens would permit a conclu- 
sion to be drawn, the segments were not penetrated by abdominal cavities ; but 
the inference is valueless, very young portions not having been examined or ap- 
parently delineated. 
The fine specimen of the chalk fossil represented by figure 29, Tab. XVIII, 
consisted of many, long, slender segments, ribbed or furrowed on the outside, 
and generally displaced ; but in a few cases they were in their right position or 
nearly so (fig. 30), and some of the lateral shoots were undisturbed and in close 
contact with the main stems (figs. 30 & 31), the whole of the evidence leading to 
the conclusion, that the intervals, if the term may be used, were exceedingly 
slight. The lateral segments necessarily sprung from calcareous portions ; but 
occasionally two issued from one termination, giving rise to a bifurcated mode of 
growth. The articular surfaces were slightly convex and concave (fig. 31), and 
concentrically furrowed with a central boss or depression. Some portions of the 
furrowed exterior (fig. 30) afforded no signs of structural hollows, but others gave 
faint indications of them ; and in following the same branch upwards, a gradual 
increase of distinctness became apparent, the upper portion exhibiting regular 
cavities with less than twelve crenulations in the boundary: other parts of the 
specimen presented similar characters. From this amount of evidence it is 
' For illustrations of the structures noticed in the text, consult Ellis and Solander’s Zoophytes, or 
Lamouroux, Exp. Méthod., tab. 3. figs. 1-4; tab. 9. figs. 3, 4; also Esper’s Pflanzenthiere, Jsts, tab. 
1,2, 3, and 3 A, 
