Geological Society. 63 
the fins of fishes had been admitted in the digits of the fin exceeding 
five, in their being sometimes bifurcated, and in consisting of an ex- 
traordinary number of ossicles; yet owing to the form of the digital 
ossicles, their breadth and flatness, and their large size, as compared 
with the joints of the fin-rays of fishes, it had been generally sup- 
posed that the locomotive organs of the Ichthyosaurus were en- 
veloped, while living, in a smooth integument, which, like that of 
the turtle and porpoise, had no other support than was afforded by 
the bones and ligaments within. 
Sir Philip Grey Egerton ina recent examination of Ichthyosaurian 
remains in the possession of Mr. Lee of Barrow-on-Soar, detected, 
with the penetration which has enabled him to bring to light many 
other obscure points in the structure of the Ichthyosaurus, traces of 
the soft parts of the fin in a slab of lias containing a mutilated pad- 
dle; and having submitted the specimen to the examination of Mr. 
Owen, a detailed account of its character forms the subject of this 
memoir. 
Mr. Owen considers the specimen to be a posterior fin of the 
Ichthyosaurus communis. It presents impressions and fractured por- 
tions of six digits, with the impression,—and a thin layer, most di- 
stinctly preserved,—of the dark carbonized integument of the ter- 
minal half of the fin, the contour of which is thus most beautifully 
defined. 
The anterior margin is formed by a-smooth unbroken well-marked 
line, apparently a duplication of the integument; but the whole of 
the posterior margin exhibits the remains and impressions of.a series 
of rays by which the fold of the integument was supported. Imme- 
diately posterior to the digital ossicles, is a band of carbonaceous 
matter of a distinctly fibrous structure, varying from two to four 
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 
