on the Genus Paleacis. 211 
val*, who obtained examples at Combe Down, near Bristol, 
from the Encrinital limestone, forming the upper bed of the 
Lower-Limestone shales. 
Lastly, Prof. Ferdinand Roemer, in the explanation accom- 
panying pl. xxix. of his ‘Lethza Palozoica’ (the text of which 
is not yet published), has a few remarks upon this subject. 
He expresses the opinion that Paleacis, EK. & H., though 
identical with Sphenopotertwm, Meek and Worthen, is not 
generically so with the group to which Hydnopora cyclostoma, 
Phill., belongs. The only difference that he mentions is that 
the corallum of the true Paleacis is regular and free, with a 
ointed base, while that of the second group is irregular and 
is attached to foreign bodies. As this second group cannot, 
of course, be referred to Hydnopora, Dr. Roemer retains for it 
the ungainly appellation of Ptychochartocyathus, Ludwig. 
We cannot, however, regard the evidence at present brought 
forward as sufficient to generically separate the two groups 
above referred to ; for, omitting many weighty reasons for our 
opinion, to be more fully entered into further on, we would 
simply point out that Meek and Worthen were themselves in 
doubt whether some, at least, of their forms were free or at- 
tached. Dr. Roemer also mentions that a comparison of 
authentic specimens of both forms has satisfied him that 
Paleacis laxa, Kunth, is the same organism*as Hydnopora 
eyclostoma, Phill. 
Having given a history of this peculiar genus and its 
species as briefly as possible, it may not be out of place to 
recapitulate in a few words the order in which the various 
points in its structure were made out. Beyond briefly descri- 
bing their respective forms, Phillips and M‘Coy can be said to 
have contributed little towards the structural details of this 
interesting group, although Phillips certainly figured dis- 
tinctly the vermicular nature of the external portions of the 
skeleton. We find that Milne-Edwards noticed the cuneiform 
appearance of the type species (a character which, by-the- 
by, is more or less traceable throughout almost all the species), 
the presence of what he considered to be numerous septa (of 
which two were thought to have been larger and more pro- 
nounced thanthe others), the supposed vermicular coenenchyma, 
and the free habit. By Edwards Paleacis was referred to the 
Madreporaria Perforata. Almost simultaneously Meek and 
Worthen published their Sphenopoterium; and, bearing in 
mind their comparison of it with Cyathoseris, they must have 
concluded it be one of the Madreporaria Aporosa. They were 
* Geol. Mag. dec. 2, vol. iii. p. 267. 
