On a new Chimæroid Fish from the Lias of Lyme Regis ( Ischyodus orthorhinus , ♂)

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Abstract
T he knowledge we have hitherto obtained of the form and structure of the fossil fishes assigned to the Chimæroid family is very limited, being derived solely from the dental plates and dorsal spines, which, from their superior hardness, have resisted the decomposition which has removed the more destructible cartilaginous structures with which they were associated. Whether these old monsters resembled the surviving members of the family in quaint form and bizarre aspect was a matter of conjecture. That they exceeded them in size is a matter of fact. The massive mandibles of Ischyodus Townshendi of the Portland age, or the enormous premaxillaries of Edaphon gigas of the Chalk era, sufficiently testify that the possessors of such powerful dental machinery must have been of heroic size compared with the surviving types of the family. The recent discovery of a specimen in the Lias of Lyme Regis, in which a considerable portion of the anterior structures of a Chimæroid is preserved, enables me to advance a step in clearing up the mystery which has hitherto shrouded this subject. It was described to me as a new species of shark, showing the dorsal spine in situ , and the upper and lower jaws. From a rough sketch of the specimen forwarded with the letter, I was inclined to think, from the peculiar mode of insertion of the spine, that it might possibly belong to a Balistes or a Siluroid fish, certainly that it could not be a shark; but on examining the specimen itself

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