150 Prof. H. A. Nicholson—Structure of Cleistopora. 
that of the plaster cast. Its total length is 148 mm., and there is 
thus a difference of only 7 mm: between the original and your 
figure. I enclose a fairly good sketch of the row of impressions on 
the left side of the telson as seen in the original. They are visible 
for a length of 57 millim. from the broken tip upwards and are 
very small, about 14 being contained within a length of five milli- 
métres.” 
Fic. 10. A small portion of the original specimen of the telson of Ceratiocaris 
Angelini, from the left-hand side, as figured in Plate V. Fig. 1. 
Magnified 4 diameters. 
I].—On vue Srrucrure or Czzisrorora (Micu@1inia) GEOMETRICA, 
Edwards & Haime, sp. 
By H. Aturyne Nicnotson, M.D., D.Sc, F.G.S., 
Regius Professor of Natural History in the University of Aberdeen. 
{* their great work upon the Paleozoic Corals (Polypiers Foss. des 
Terr. Pal. p. 252, pl. 17, figs. 3, 8a, 1851) Milne Edwards and 
Haime describe and figure, under the name of Michelinia yeometrica, 
a remarkable little Coral from the Devonian rocks of France. By 
the kindness of Dr. Daniel Gihlert, of Laval, whose researches upon 
the stratigraphy and paleontology of the French Devonian rocks 
are well known, I have been enabled to examine some well-preserved 
examples of this interesting form, and have determined some new 
facts as to its internal structure. Investigation by means of thin 
sections has, in fact, shown that this Coral has in reality no close 
relationships with the genus Michelinia, but that its affinities are 
rather with Protarea, EK. & H. It differs, however, in important 
~~structural features from Protar@a, and appears to form the type of a 
( new genus to which the name Cleistopora may be given. 
Cleistopora geometrica, K-and H. sp. (Fig. 1, A), is a little discoid 
Coral, averaging from one and a half to two centimétres in diameter, 
from two to three millimétres in thickness in the middle, and 
usually attached parasitically to a Brachiopod or other foreign body. 
In some cases it appears to have been free. The short vertical 
corallites terminate in shallow hexagonal calices, which are mostly 
from five to six millimétres in diameter. The floor of each calice 
is formed by a flat or slightly convex surface, more or less clearly 
reticulated, which was regarded by Milne Edwards and Haime as 
being constituted by the highest of the ‘“tabule,” which they sup- 
posed to possess a strongly granulated exterior. Examination by 
means of thin sections (Fig. 1, C) shows, however, that “tabule ” 
are entirely wanting, and that the whole visceral chamber, below 
the level of the calice, is occupied by a mass of reticulate or tra- 
becular tissue, formed by irregularly anastomosing calcareous fibres. 
