154 Royal Society : — 



absent, or at all events rudimentary only. In the Favositidse the 

 septa seem to have been no more perfect than they are in Helio- 

 pora, and to have been most variable in number, but often twelve, 

 as also in Heliopora. M,-Edwards describes from 10 to 12 septa 

 in Favosites gothlandica. In Michelinia favosa 30 to 40 subequal 

 septal striae are to be made out at the upper margin of the wall 

 of the calicle. I cannot refer to specimens ; but it seems not 

 unhkely that the s?pta in the Pavositidae were pseudo-septa as in 

 Heliopora, and that these coralla were formed by Alcyouarians, the 

 perforations in the walls having transmitted transverse canals like 

 those of HeliojwraandSarcojihi/ton, and the coralla being free of tabu- 

 lar coenenchym, because none of the polyps were aborted as in 

 Heliopora. Some Favositidae seem to have formed a compound 

 colony, consisting of polyps and zooids, as Favosites Forhesii, where 

 a few large cells are seen set amongst numerous surrounding small 

 ones. Heliolites seems to a certain extent to form a transition 

 stage between a condition such as that in Favosites Forhesii and 

 the condition in Heliopora ; for in Heliolites, the more ancient form, 

 the coenenchymal tubes are regularly hexagonal, and apparently 

 much more nearlv 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 0])en, 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 coenenchymal 

 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 Alcyonarian, Chcetetes was of course also 

 of that group. The genus Alveolites amongst the Favositidae is 

 peculiar for the possession of three tooth-like 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 in 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 Alcyonarians, 

 and the direction of all the " Dorsalf iicher " in Sarcophyton and 

 Heliopora towards the central axis of the colony. In Alveolites the 

 two teeth seem to correspond to the " Dorsalfach," and the suigle 

 one to the " Ventralfach," the two teeth having occupied the space 

 devoid of retractor muscles. Kolliker describes a series of teeth 

 as existing at the margin of the caKcle in Renilla, which follow a 

 constant law in their relation to the septa. When only one tooth 

 is present it is opposite the " Dorsalfach ;'' when three, one is op- 

 posite the " Dorsalfach," and the two others opposite the lateral 

 " Ventralfach." In Alveolites the one tooth is ventral instead of 

 dorsal. In Syringopora the septa seem to be very much of the 

 same nature as in Heliopora ; and in Heliojiora, as already described, 

 the tabulae are not merelv transverse floors, but the bottoms of 



