Murchison—Laurentian Rocks. 147 
linch to 13 inch. Each vertebra has a long flattened spine 
upwards of 35 inches in length. The snout apparently was 7 inches 
in length; the teeth not seemingly all of the same length, and at 
irregular distances between each other. 
The ‘cup-shaped vertebre,’ no doubt, indicate the deeper 
conical cavity of the terminal articular surface of the centrum, 
which distinguishes that part of the skeleton of the fish from 
the vertebre of amphiccelian Crocodilia, of which, by the way, 
we have hitherto had no evidence in formations more recent 
than those of secondary geological age. 
Like the Pachyrhizodus, the present Miocene Fish is most 
probably a Cycloid with sauroid dentition. The almost cir- 
cular section of the teeth differentiate it from the large extinct 
‘ Sphyrenoid Cycloids, Sphyrenodus, Hypsodon, Saurodon, 
Saurocephalus, &c. It differs, by so much of the dental cha- 
racter as opportunity has been given me of comparing, both 
specifically and generically, from Pachyrhizodus basalis; and 
I propose to indicate this fine addition to Miocene Tertiary 
Vishes by the name of Stereodus* Melitensis. It is much to be 
desired that the rest of the skeleton of this extinct Fish should 
be figured. 
IJ. A FEW morE WoRDs ON THE LAURENTIAN ROCKS, AND THE 
PROOFS OF THEIR EXISTENCE IN BRITAIN. 
By Sir Roprericx I. Murcutson, K.C.B., F.R.S., &e. 
i my observations on the Laurentian Rocks of Britain which 
appeared in the last number of the GroLocicaL Magazine, 
there is one statement which calls for modification, and another 
which I revoke. ‘The striking discordance of direction or strike 
between the true Laurentian rocks of the North-Western Highlands 
and Islands, and the superficial strata of Cambrian and Lower 
Silurian age as described by me, is undoubtedly correct; but in 
another paragraph it is inadvertently said that the Silurian rocks 
of Britain trend everywhere from NE. to SW. For ‘everywhere’ 
the word ‘usually’ should have been employed, as there are tracts 
wherein these rocks unquestionably range from W. to E. 
The essential point, however, to which I now call the attention 
of geologists is, that on reviewing my own notes upon and sections 
of the Connemara Mountains of Ireland (made in 1851), I am quite 
satisfied that the green serpentinous marble of that district, in which 
a Foraminifer supposed to be the Hozoon Canadense is found, is 
unquestionably of Lower Silurian age, and is not, as was surmised 
it might prove to be, a true Laurentian rock. 
My friend Professor Harkness, who has examined this tract more 
recently than myself, has written to me expressing his conviction 
* From otepeds, solidus ; d50vs, dens. 
L 2 
