On Ascension-Island Zoology. 439 
of that genus, but differs from any species hitherto assigned 
to it in the small size and very slight depth of the calices. 
It differs further in its spongy columella so much from the 
typical forms that it is excluded from the genus as limited 
Fig. 1. 
Fig. 1. Platygyra ascensionis. A few calicles, asseen from above, Xx 4. 
Fig. 2. Ditto. A wide calicle in vertical section, made outside the 
columella, which is seen beyond line of section, x 4. 
(under the appellation Celoria) by Milne-Edwards & Haime 
(Hist. Cor. 1. p. 411); but Dr. Briiggemann has given 
reasons (“Corals of Rodriguez,” Phil. Trans. vol. elxviii. 
p-571) for considering the character, whether vertical or spongy, 
of this part not to be even of specific importance, having been 
obliged to unite under the name Platygyra Esperi forms which 
have both vertical and spongy columelle. This species has the 
calicles much more individualized than is usual in that species, 
and in this respect appears to approach the Faviacez, and 
may perhaps mark a transition to that group; but it is very 
decidedly distinct in other points from the genera of that 
group as at present known and under their present limitations. 
Of the species referred doubtfully to Prionastreea by Milne- 
Edwards & Haime (Hist. Cor. i. pp. 522-525), I believe 
both Astrea rigida and A. varia, Dana, to be referable to 
this section of Platygyra: the former, coming from the East 
Indies, seems to be the nearest known ally of this form out of 
the Atlantic area; and the latter (A. varia), from the West 
Indies, the nearest from the Atlantic region. Some forms of 
P. Espert trom Rodriguez Island also approach it, but not 
closely. 
