82 REPORT—1858. 
which gave rise to these breccias; and as no other force capable of transporting 
angular fragments a considerable distance at present operates except ice, it becomes 
necessary to refer the presence of these breccias to the same cause which gave rise to 
those of Worcestershire and Shropshire. The absence of the grooves and striz from 
the fragments which compose the Dumfriesshire breccias, indicates that the mode of 
operation of the ice was somewhat different in these from those occurring in Wor- 
cestershire and Shropshire. Glaciers seem to have had their influence in producing 
the deposits in the latter areas, whilst in the former the ice seems to have acted prin- 
cipally as a raft, transporting rocky fragments from one area to another. ‘The cir- 
cumstances which the breccias of the southern portion of the Vale of the Nith present, 
seem to justify the conclusion of Professor Ramsay, that glacial conditions obtained 
during part of the Permian epoch. 
Observations on the Genus Pteraspis, By Tuomas H. Huxtey, F.R.S., 
Professor of Natural History, Government School of Mines. 
In a paper “ On Cephalaspis and Pteraspis,” recently read before the Geological 
Society, and published in the ‘ Quarterly Journal’ for the present year, I endeavoured 
to prove,— 
fot. That the Cephalaspis Lloydit and Lewisit of the author of the ‘ Recherches 
sur les Poissons Fossiles,’ subsequently united into a distinct genus, Péeraspis (Kner), 
were rightly judged by Prof. Agassiz to be the remains of fish, and that they are not, 
as had been imagined by other naturalists, either Crustacean or Molluscan. 
2nd. That, as Prof. Agassiz had surmised, they are at once allied to Cephalaspis, 
and generically distinct from it. 
I grounded these conclusions almost wholly on histological evidence, or that afforded 
by the microscopic structure of the bodies in question. Not having seen the Cepha- 
laspis rostratus of Agassiz, I abstained from offering any opinion with regard to it. 
Since the publication of my paper a great deal of new material has passed into my 
hands, chiefly by the kindness of the zealous geologists and paleontologists who reside 
in and about Ludlow, Messrs. Cocking, Crouch, Harley, Lightbody, Marston, and 
Salwey, and I have thereby been enabled greatly to extend and confirm my conclu- 
sions with regard to the nature and affinities of these remarkable extinct fishes. A 
brief note of the results at which I have now arrived will perhaps be interesting to 
the Section. 
The oblong plates which have hitherto been the only discovered parts of Pteraspis, 
form only a portion of the great shield which covered the anterior part of the dorsal 
region of the body. Apparently anchylosed or continuous with the anterior edges of 
some specimens of these plates, there is a bony disk, prolonged at its postero-lateral 
angles into two long cornua, which pass into the edges of the oblong plate. The disk 
exhibits the characteristic structure and the peculiar striated sculpture; it is prolonged 
anteriorly into a sort of rostrum, whose length varies with the species of Pteraspis: 
laterally it exhibits two well-marked nearly circular marginal apertures, which I 
make no doubt are the orbits. 
I conceive, therefore, that the part in question corresponds with the anterior part 
of the cephalic disk of Cephalaspis, and that the oblong plate, which may well be 
termed the occipito-nuchal plate, answers partly to the posterior moiety of the cephalic 
disk of Cephalaspis, partly to that median backward prolongation of. the posterior 
margin of the cephalic disk of Cephalaspis to which I have particularly directed at- 
tention in my memoir. It is from this that the strong nuchal spine of the Cephalaspis 
arises; and as if to render the resemblance complete, the most perfect specimens of 
Pteraspis show that it had a like spine developed in a similar position. 
There exists, indeed, a most interesting gradational series of forms between Cephal- 
aspis Lyellit and Pteraspis. 
The Auchenaspis of Sir Philip Egerton has a cephalic disk with the semicircular 
anterior outline of that of Ceph, Lyellii, but the interspace between the cornua of the 
disk is nearly filled up by the large nuchal plate, whose backward extent may have’ 
been greater than is exhibited by any of the specimens of Auchenaspis yet obtained. 
Enlarge the nuchal plate of Auchenaspis and give the cephalic disk a more produced. 
anterior outline, and the result is the form of Péeraspis. : 
