124 THE VOYAGE OF H.M.S. CHALLENGER. 
are in Heliopora, and to have been most variable in number, but often twelve, as also in 
Heliopora. Milne-Edwards describes from ten to twelve septa in Iwvosites gothlandica. 
In Michelinia favosa thirty to forty subequal septal striae are to be made out at the 
upper margin of the wall of the calicle. It seems not unhkely that the septa in the 
Favositidee were pseudo-septa as in Heliopora, and that these coralla were formed by 
Alcyonarians, the perforations in the walls having transmitted transverse canals of soft 
tissue like those of Heliopora and Sarcophyton, and the coralla being free of tubular 
coenenchym, because none of the polyps were aborted as in Heliopora. Some Favositidee 
seem to have formed a compound colony, consisting of autozooids and siphonozooids, for 
example, Favosites forbesi, in which a few large cells are seen set amongst numerous 
surrounding small ones. eliolites seems to a certain extent to form a transition stage 
between a condition such as that in Favosites forbesi and the condition in Heliopora ; 
for in Heliolites, the more ancient form, the ccenenchymal tubes are regularly hexagonal, 
and apparently much more nearly equal in breadth to the calicles than in Heliopora. 
In the growing points of Heliopora the hard parts are made up of a series of open often 
hexagonal tubes, and resemble Favosites in their surface aspect. In Heliopora the 
transverse canals pass over notches in the summits of the walls of the coonenchymal tubes 
and calicles, in order to place these cavities in communication with one another. In 
Favosites the calcareous tissue surrounded the transverse canals, and the perforations in 
the walls of the calicles were thus produced. 
If Favosites was an Aleyonarian, Chetetes was of course also of that group. The 
genus Alveolites amongst the Favositidee is peculiar for the possession of three tooth-lke 
prominences as the only representatives of septa. One tooth, well developed, is situate 
inside the calicle ; on that side of each calicle which lies externally m the colony, and 
opposed to this on the tip of the calicle next the interior of the colony, are a pair of 
rudimentary teeth. This arrangement reminds us at once of the distinction of dorsal and 
ventral mesenterial interspaces in Aleyonarians, and the direction of all the ‘‘ Dorsalfiicher ” 
in Sarcophyton and Heliopora towards the central axis of the colony. In Alveolites the 
two teeth seem to correspond to the “ Dorsalfach,” and the single one to the “ Ventral- 
fach,” the two teeth having occupied the space devoid of retractor muscles. Koélliker 
describes a series of teeth as existing at the margin of the calicle in Renilla, which follow 
a constant law in thei relation to the septa. When only one tooth is present it is 
opposite the “ Dorsalfach ;” when three, one is opposite the ‘ Dorsalfach,” and the two 
others opposite the lateral “ Ventralfach.” In Alveolites the one tooth is ventral instead 
of dorsal. 
Alliance of Syringopora with Tubipora.—n Syringopora the septa seem to be very 
much of the same nature as in Heliopora; and in Heliopora, as already described, the 
tabulz are not merely transverse floors, but the bottoms of cups of hard tissue fitted 
inside the older tubes and calicles. In Syringopora this condition of the tabule is much 
