Millepora and Stromatopora. 311 
the Plutonic one, it will be quite time to speculate as to its 
original nature; till then it must remain in the abode of 
omne tgnotum pro magnifico, into which science forbids her 
votary to enter. (The specimen of Hozoon to which I have 
alluded (a slice about 24 x2 inches), was sent by Dr. Car- 
penter to Profs. King and Rowney, of the Galway College, 
Ireland, who kindly presented it to me.) 
EXPLANATION OF PLATE XVII. 
Fig. 1. Hydractinia arborescens, n. sp. on a turreted shell. Natural 
size. Branches of the specimen broken off. aa, branches; 
b, largest branch ; c, apex of the shell exposed, from a portion 
of the polypary having been broken off; d, lip of shell trans- 
formed into polypary, also broken. 
Fig. 2. The same. Diagram of portion of surface of the polypary, to 
show:—a a, large branch of the grooved venation passing through 
the surface ; 66, apertures of the polypites, &c.; ¢c¢, lines indi- 
cating the position of the grano-serrulated ridges of the polypary. 
Scale about 1-96th to 1-1800th inch. 
Fig. 3. The same. Diagram of portion of surface of polypary, more mag- 
nified, to show :—a a, apertures of polypites &c. in relation to 
bb, grano-serrulated ridges. Scale about 1-48th to 1-1800th 
inch. 
Fig.4. The same. Diagram of portion of surface of polypary, to show 
the grooved venation only. Magnified about 2 diameters. 
Fig. 5. Millepora alcicornis. Diagram of portion of corallum including 
vertical section of part of a tubular space. Much magnified. 
aa, tubular space; 66, ccenosarcal skeleton; ¢, transverse 
septa or tabule ; d, apertures of the cancelli in the ccenosarcal 
skeleton ; e, the same, opening into the tubular space. Trans- 
verse diameter of tubular space about 1-120th inch. 
Fig. 6, Millepora Woodwardii. Surface of upper half. Natural size. 
a a, systems of stelliform venation. [N.B. For the description of 
this fossil see ‘Annals,’ 1877, vol. xix. p. 64, under the provi- 
sional name of “ Bradya tergestina, Stache, MS.” } 
Fig.7. The same. Horizontal section. Natural size. a, horizontal 
section of tubular spaces at the centre ; 6, oblique section of the 
tubular spaces at the circumference. 
Fig. 8. The same. Diagram of a portion of the surface, much magnified, 
to show the fossilized fragments of a superficial tubulation like 
that appearing above the outer layer on some parts of Millepora 
alcicornis. a, branches of tubulation; 0, subjacent apertures 
of calicles or tubular spaces. Scale about 1-48th to 6-1800ths 
inch. 
Fig.9. The same. Diagram of portion of the corallum, including a ver- 
tical section of part of a tubular space bearing septa or tabule. 
More magnified. aaa, radiating tubular spaces; 06, cceno- 
sarcal skeleton between the radiating tubular spaces ; ¢, trans- 
verse septa or tabule; d, apertures of the ccenosarcal skeleton in 
the tubular space ; e, surface of corallum. 
Fig. 10. Stellispongia variabilis, D’Orb., from the Trias. Traced from his 
figure (Cours élément. de Paléontol. et Géologie, vol. i. p. 214, 
fig. 388). aa, systems of stelliform venation; 6, portion of 
surface, more magnified, 
