158 
lines in breadth, and extending in an obtusely-pointed form for an 
inch and a half beyond the digital ossicles. This band Mr. Owen 
believes to be the remains of the dense ligamentous matter which 
immediately invested the bones of the paddle, and connected them 
with the enveloping skin. The rays, above mentioned, are continued 
from the posterior edge of this carbonized ligamentous matter, in 
which their bases appear to have been implanted, to the edge of the 
tegumentary impression; the upper rays being directed transversely, 
but the others gradually lying more in the direction of the axis of 
the fin, as they approach its termination. The most interesting 
feature in these rays, Mr. Owen says, is their bifurcating as they 
approach the edge of the fin. 
From the rarity of their preservation, their appearance and co- 
existence in the present instance with remains of the integument, 
he states, it is evident they were not osseous, but probably either 
cartilaginous, or of that albuminous horn-like tissue, of which the 
marginal rays consist in the fins of the sharks and other plagio- 
stomous fishes. Besides the impression of the posterior marginal 
rays, the specimen presents a series of fine, raised, transverse lines, 
which cross the whole fin, and probably indicate a division of the 
rigid integument into scutiform compartments, analogous to those 
on the paddle of the Turtle and webbed foot of the Crocodile; but 
they differ in the absence of subdivision by secondary longitudinal 
impressions. The structure of the integument of the fin agrees, 
therefore, with the known reptilian characters of the skeleton of the 
Ichthyosaurus ; and, as the skin with its appendages gives a charac- 
ter to the great primary groups of vertebrata, it might be expected 
that the skin of the Ichthyosaurus would exhibit some of the cha- 
racters of the integument of existing reptiles. 
In conclusion, Mr. Owen remarks, that the other new facts pre- 
sented by the specimen, accord with the indications of the natural 
affinities of the Ichthyosauri afforded by their less perishable re- 
mains ; and that all the deviations from the reptilian structure of 
the skeleton, tend to the type of fishes and not to that of cetaceous 
remains. 
A paper was afterwards read on as much of the great graywacke 
system as is comprised in the group of West Somerset, Devon, and 
Cornwall, by the Rev. D. Williams, F.G.S. 
This communication is supplementary to one read in April 1839*, 
and contains the results of the author’s last investigation into the 
structure of country. Before he details his present views, he cor- 
rects what he conceives was an errorin his former paper, and states, 
he is now convinced that the slates and limestones of South Devon 
and Cornwall are not a prolongation of the trilobite slates (No..7)t 
*® See ante, p. 115. 
+ The following is the descending arrangement given in Mr. Williams’s 
former paper: 9, floriferous slates and sandstones (culm measures); 8, Cod- 
don Hill grits; 7, trilobite slates; 6, Wollacomb sandstones; 5, Morte 
slates; 4, 'Trentishoe slates ; 3, calcareous slates of Linton; 2, Foreland 
or Dunkerry sandstone; 1, Cannington Park limestone, see ante, p. 116, 
