Geological Society. 173 - 
land, and received by the author from Dr. George Bennett. Its 
principal differences from Diprotodon are that it has no depression 
above the outer condyle, but in its place a rough longitudinal rising 
for the attachment of the same or of a homologous muscle; and 
the hinder surface of the outer condyle is transversely convex. The 
relative width of the post-condylar fossa resembles that in Phasco- 
lomys; and a further resemblance to the Wombats consists in the 
more equal prominence of the lateral boundaries of the rotular 
surface than in Diprotodon and Macropus. The bone differs from 
the corresponding part in the Wombats by several subordinate cha- 
racters; and the animal to which it belonged would seem to have 
been intermediate between Phascolomys and Macropus. From the 
size and characters of the bone the author referred it to Nototherium 
Mitchelli ; its breadth across the condyles is 52 in. 
3. “On Helscopora latispiralis, a new spiral Fenestellid from 
the Upper Silurian beds of Ohio, U.S.” By E. W. Claypole, Esq., 
B.A., B.Sc. (Lond.), F.G.S. 
The author referred to the genus Archimedes, recognized by 
Lesueur, D. D. Owen, and James Hall, as a spiral form of Fenes- 
tellid, the remains of several species of which occur in Lower Car- 
boniferous Limestone rocks in the United States. In Archimedes 
there is always a strong central shaft. The species here described 
by the author under the name of Helicopora latispiralis occurs in 
the Upper beds of the Niagara group of the Upper Silurian at Cedar- 
ville, Ohio; and the new genus is distinguished from Archimedes by 
the absence of the solid stony axis above mentioned. Its character 
as given by the author is as follows :—‘‘ Polyzoary expanded, fenes- 
trate, and spiral, formed of slender bifurcating branches poriferous 
on one face, connected by non-poriferous bars, forming an open net- 
work ; cells arranged in two rows along the branches, one row on 
each side of a median keel. Axis very thin, or consisting only of 
the thickened central border of the spiral polyzoary.” The species 
described grows to as much as eight inches in diameter. The 
author has seen a second species of the genus. 
June 21, 1882.—J. W. Hulke, Esq., F.R.S., 
President, in the Chair. 
The following communications were read :— 
1. “On Thecospondylus Horneri, a new Dinosaur from the 
Hastings Sand, indicated by the Sacrum and the Neural Canal of 
the Sacral Region.” By Prof. H. G. Seeley, F.R.S., F.G.S8. 
The author described a mould of the neural canal of the sacral 
region of a Dinosaur, obtained by Dr. A. C. Horner, of Tonbridge, 
from a quarry in the Hastings Sand at Southborough. Thespecimen 
is about 2 feet long, slightly imperfect at both ends, but showing 
indications of five complete vertebrae, with traces of others at the 
two extremities, making at least seven vertebra in all. The general 
