REPORT ON THE REEF-CORAIS. 139 
close and thick, radiating structures, which are divided up into strong spines or teeth, 
so as to be stoutly and crowdedly echinate. In fact, the condition of the wall and coste, 
in this compound form, exhibits the closest resemblance to that which obtains in the 
simple genus Fungia, a form from which Halomitra may at once be derived by the 
development of secondary or daughter calicles around the central primary calicle. 
Comparing this characteristic condition of Halomitra with that which obtains in the 
species for which the genus Podabacia was instituted by Milne-Edwards and Haime, 
namely, the Madrepora crustacea, Pallas (=Pavonia explanata, Dana), we find an 
essential and fundamental distinction. This was clearly recognised by Dana, who states 
that the under surface is “‘echinulato-striate and porous,” that is, that the wall is not 
solid, but finely and closely porous or fissured throughout, while the coste are in the 
form of distinct striations, the course of which is indicated by the fine denticulations or 
echinulations of which they are composed, and the radial arrangement of which is 
generally much obscured : a condition comparable to that which obtains in Lithactina 
rather than in Fungia. 
Concerning this form (Pavonia explanata, Dana= Podabacia crustacea), Dana 
writes: “this species might well form a distinct genus. It looks much like an inverted 
Halomitra,” a statement that is altered to a considerable extent by Milne-Edwards and 
Haime, who, in writing of the same species, say, “il se trouve indiqué dans l’ouvrage 
de M. Dana, qui le définit trés-justement en l'appelant une Halomitre retournée et pédon- 
culée.” The genus Podabacia was certainly well instituted for this very distinct form. 
The confusion between the genera Podabacia and Halomitra has arisen from the 
fact that there exist specimens which, while they have the characteristic shape of 
Halomitra pileus, yet possess the structure of Podabacia crustacea, as exemplified in the 
characters of the wall and costs: specimens which are clearly referable to Podabacia 
(amended so as to include free as well as fixed forms). 
From this it will be seen that we have no means of determining whether the Mitra 
polonica of Rumphius, which is usually regarded as being the Halomitra pileus, 1s 
really referable to Halomitra or Podabacia. 
The Halomitra pileus of Dana is undoubtedly the Madrepora pileus of Pallas, 
whose description must certainly have been drawn up from a specimen of Halomutra 
and not of Podabacia. The description of Lamarck would apply equally well to either 
of the equiform specimens of Halomitra and Podabacia, and have included them both ; 
while the redescription of Milne-Edwards and Haime was evidently drawn up from 
specimens of both of these types and is more applicable to the Podabacia than to the 
Halomitra form. 
So that while, on the one hand, the specific term pilews must apply to the 
Halomitra (Madrepora) pileus, Pallas (= Halomitra pileus, Dana), it is desirable, on the 
other hand, to retain it also for the equiform Podabacia, which would, therefore, stand 
