40 K. J. CHAPMAN ON THE 



ClaS8 II. Hijdrocoralla. 

 A.- — Stomach partially separated from body-cavity. 

 {i) — Oro-aual orifice with eight fringed tentacles : 



Class III. Akyonaria or Crossocoralla. 



(ii) — Oro-anal orifice with mimerons simple tentacles. Corallnm essentially 

 non-taljulated, but with distinct septa : 



CijASS IV. Zountharia or Anlhucorul/a. 

 B. — With natatory cilia : 



CIjASS V. Ctenophwu. 



The present communication refers essentially to the second of the above named 

 classes — that of the Hydrocorall.4. This includes the Hydro-CoraUiinr of Moseley, 

 together with the so-called Tabulata and Rugosa oï other classifications. In the present 

 state of our knowledge it is necessarily to some extent a group of convenience, connecting 

 the Hydfotoa with the typical corals. The Tabulata in many classifications are widely 

 separated from the Rugosa, and placed with the ordinary " Hexamerous Corals :" although, 

 from the absence or rudimentary character of septa in many of these forms it is not pos- 

 sible to tell whether the tentacles of the living animal were hexamerous or otherwise. 

 The Rugosa are also for the greater part essentially tabulated forms ; and although, 

 commonly separated from the Tabulata under the name of Tetracoialla, the actual number 

 of septa in many cases is either indeterminable or exceedingly variable. As examples of 

 variation in the number of septa in both the Tabulata and Rugosa, the genera Sli/lina, 

 Lamarck, Stylocœnia, Edwards and Haime ; Heterophylliu, McCoy ; Duncanella, Nicholson, 

 and many others, may be cited. The descriptions of many Canadian species by the late 

 Mr. Billings, a most minute and trustworthy observer, also substantiate this point, and 

 prove that, although very convenient on paper, the distinction (except in certain well 

 marked cases) is virtually of impossible application. And again, we have no certainty 

 that the number of septa or septal markings really indicate the number of the tentacles 

 possessed by the living animal. In the living Millepora, for example, the researches of 

 Moseley have shown the presence of eight tentacles, as in the Alcyouarians. If therefore, 

 as commonly assumed, the fossil Heliolites be regarded as a closely related type, its twelve 

 septa or " pseudo-septa " are entirely misleading. 



Many of the forms placed under this subdivision in the present synopsis — especially 

 those of the three first sections given below — may very probably belong to the Akyonaria 

 or to the Bryozoa; but this view is entirely conjectural, and cannot at present be either 

 proved or disproved On the other hand, the strikingly tabulated structure, so charac- 

 teristic of the great majority of these forms, serves to unite them conveniently, and, in 

 the absence of negative evidence, naturally also, into a common group. 



The class Hydrocoballa, as here adopted, may therefore be defined as follows : — 

 Hydrozoa or closely allied types with calcareous corallum. The cells of the latter either 



