COEEESPONDENCE. 
451 
Restoration of JBterasfis, 
My dear Sie, — I have read the Eev. 
H. Mitchell's paper on " The Restora- 
tion of Pteraspis " with great interest, 
but the conclusions he dravt s from his 
Scotch specimens are, I think, by no 
means borne out by examples obtained 
from English localities. I enclose you 
two sketches of Pteraspids from Crad- 
ley, in Herefordshire : one, in my own 
collection, showing the anterior portion 
of the shield ; the other, exhibiting the 
posterior portion and surface markings, 
in the possession of Mr. Gregory, of 
Golden Square. These two sketches 
will be sulBcieiit to show that the shield, 
as drawn by Mr. Mitchell, is wanting in 
some important particulars ; the true 
form I believe to be that given in fig. 3. 
Mr. Mitchell seems to be under the im- 
pression that the restoration of Pteraspis 
has never before been attempted, al- 
though first-rate specimens have been 
in our museums and private collections 
for some years. Professor Huxley, in 
vol. xvii. of Geol. Soc. Journal, has given 
a diagram of a restored Pteraspis, which 
is copied in fig. 3 ; he has likewise re- 
ferred to the subject in British Asso- 
ciation Reports, 1858, and has further 
written a detailed account of the microscopic structure of the test in vol. 
xiv. of the Journal. The references in fig. 3 are as follows : — a is the snout 
or rostrum, united with h, the shield-like 
disk ; c c are the lateral cornua attached to 
the disk ; e is the posterior spine, and/" f are 
the orbits or perhaps the nasal apertures. 
The corresponding parts can be easily found 
in the sketches I have given of the fossil 
Pteraspids. I may just mention here, that 
the bonelike test of these fish is composed of 
three layers, — an external, finely striated 
layer, a middle cancellated layer composed 
of polygonal cells, and a third internal 
layer of a laminated nacreous substance. 
Tne specimen drawn in fig. 2 shows the 
external layer remarkably well ; in fig. 1, 
parts of the middle cancellated layer may 
be seen ; the rest of the test, which is pre- 
served, being the internal nacreous layer. 
I remain, dear Sir, yours truly, 
E. K. Lankester, 
8, Savile Row, Nov. 9. 
P.S. — You will observe some minute in- 
dentations drawn in fig. 2, on the surface Fig. 2. 
Fig. 1. 
