190 A. E. Verrill—Affinities of Paleozoic 
In the present state of science, the only stony corals which 
are known to be formed by hydroids are the several species of 
Millepora. We can reasonably infer that a few other genera 
having essentially the same structure, or belonging properly to 
the same family, are also the corals of hydroids. But as to the 
great majority of the “ Tabulata” and “ Rugosa,” there can no 
longer be any reasonable doubt that they were made by true 
polyps, essentially similar to those of the existing corals. 
But among the Tabulate corals, after excluding the Millepo- 
ride, great diversities of structure still remain, and no doubt 
representatives of several families that ought to be widely sepa 
in the tropical waters of the Pacific and Indian oceans. 
corals are terized by rather small, tubular cells, usually 
* The following quotation from the Bulletin of the Mus. of Comp. Zodlogy, » 
No. 13, p. 384, Nov., 1869, will serve to illustrate the views of Professor AgassiZ: 
: we now remember that the Acalephian affinities of the Tabulata are unques- 
tionable, and that, with them, the Rugosa must be removed from the class of 
ng : 
