488 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 11, 
those organs, and that they probably represent the apodemata, or 
infoldings, of the hard external crust to which those organs, or the 
muscles by which they were moved, were attached. 
The prominence of the hypostome in the Trilobita reminds one 
even more strongly of the genus Apus than of the Isopods ; and it is 
quite reasonable to expect, in the Trilobita, a more generalized type 
of structure than that which marks the modern representatives of 
the class. 
The question will naturally be asked why so many specimens of 
Trilobites should be found, yet no traces of limbs. It seems reason- 
able to infer that a large number of these fossil remains are only 
exuvie, the Crustacea frequently casting their shells. The detach- 
ment of the limbs is also a common occurrence in all the fossil 
Articulata, especially where, as in the Crustacea, the proximal joint 
is extremely constricted, and, in consequence, easily disarticulated. 
' Nor need we assume that all the genera of this very extensive 
family had horny or chitinous limbs, seeing that in the modern 
Isopoda a great diversity exists in these organs. 
With regard to the section of Calymene senaria exhibited, it 
seems difficult to accept the suggestion that these are the eggs of 
the same Trilobite, seeing that they fill the entire cavity of the test, 
as shown in the section. 
The publication of Mr. Billings’s discovery appears to me to be 
of the highest importance to paleontologists ; and he is entitled to our 
best thanks; for his observations are sure to excite further researches 
upon the Trilobita, and thus will be the means of greatly increasing 
our knowledge of this interesting group. 
3. On the SrrvcturE and Arrryirins of SicttLARIA, CALAMITES, and 
CatamopEnpRron. By J. W. Dawson, LL.D., F.R.S., F.GS., 
Principal and Vice-Chancellor of M‘Gill University, Montreal. 
(The publication of this paper is deferred.) 
[ Abstract. | 
The object of this paper was to illustrate the structure and affi- 
nities of the genera above named, more especially with reference to 
the author’s previous papers on the “ Structures in Coal” and the 
“Conditions of Accumulation of Coal,’ and to furnish new facts 
and conclusions as to the affinities of these plants. 
With reference to Sigillaria, a remarkably perfect specimen of the 
axis of a plant of this genus, from the Coal-field of Nova Scotia, was 
described as having a transversely laminated pith of the Sternbergia 
type, a cylinder of woody tissue, scalariform internally and reticu- 
lated or discigerous externally, the tissues much resembling those 
of Cycads. Medullary rays were apparent in this cylinder; and it 
was traversed by obliquely radiating bundles of scalariform vessels 
or fibres proceeding to the leaves. Other specimens were adduced 
to show that the species having this kind of axis had a thick outer 
