FOSSIL HYDROZOA. 



173 



pora antigua of the Tertiary of France). The family in- 

 cludes several genera (Stylaster, Allopora, CryptoJielia, &c.), 

 all of which secrete a branched calcareous skeleton, so 

 closely resembling some undoubted corals (such as Oculina) 

 that the group has always been regarded as referable to the 

 Oculinidce. Taking Stylaster (fig. 66) as the type of the 



Fig. 66. A, Portion of the skeleton of Stylaster sanguineus, of the natural size ; B, Small 

 portion of a branch of the same, enlarged, showing the calices and ampullae. Living in the 

 Australian seas. (After Milne-Edwards and Haime.) 



group, we find the skeleton to be a branched calcareous 

 structure, studded at intervals with cup - like depressions, 

 each of which exhibits a central chamber, occupied axially 

 by a styliform rod (" columella "), and surrounded by a series 

 of secondary chambers, separated from one another by short 

 partitions (" septa "), which appear to be formed by a folding 

 of the wall. Though the general appearance thus produced 

 especially as regards the existence of " calices " and 

 " septa " - is distinctly that of the ordinary compound 

 corals, yet Mr Moseley has shown that the animal forming 

 this skeleton is truly a composite Hydroid. The colony 

 consists of two sets of zooids, of which the larger and per- 

 fect ones inhabit the central chambers of the calices, while 

 the smaller chambers, marked off by the septa, are occupied 

 by rudimentary and imperfect zooids, resembling tentacles in 



