Geological Society. 



G3 



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 in a 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 



