40 E. .1. CHAPMAN ON TIIH 



CljAt-'S II. Hijdrucoralhi. 

 A.- — St'UiiacJi partially separated from body-cavity. 

 (t ) — Oro-aual orifice with eight fringed tentacles : 



CiiASS III. Alcyimaria or Crossoro^ratla. 



(ii) — Oro-iinal Drilice with luimerous simple tentacles. C'unillum e^ss^'lltially 

 iioii-tabulated, but with distinct septa ; 



Cj>ASS IV. Zonntltaria or Anlhocordlht. 

 B. — AV4th natatory lilia : 



CJiAS8 V. Ctenoplioni. 



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

 classes — that of the Hydrocorali-.\. This includes the Hydro-CoralJimc of Moseley, 

 together with the so-called TabuJata and Riigosa of other classifications. In the present 

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

 the Hi/dro:t>u with the typical corals. The Tubu/ata in many classifications are widely 

 separated from the Riigosa, 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 Rugom are also for the greater part essentially tabulated forms ; and although, 

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

 of septa iu many cases is either indeterminable or exceedingly variabb'. As examples of 

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

 Lamarck, Sti/loarnia, Edwards and Haime ; Helero/ihylfia, McCoy ; Diincanella. 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 lubstautiate 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 Mi/le/)ora, for example, the researches of 

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

 as commonly assumed, the fossil HelioUtes 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 — espei ially 

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

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

 l>roved or disproved On the other hand, the strikingly tabulated structure, so charai- 

 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 oroup. 



The class HviiROCOllAT.LA, as here adopted, may therefore be defined as follows : — 

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



