BRITISH FOSSILS. 



Decade X. Plate IX. 



DIPLACANTHUS GRACILIS. 



[Genus DIPLACANTHUS. Agassiz. (Sub-kingdom Vertebrata. Class Pisces. 

 Order Goniolepidoti. Family Acanthodei.) Body fusiform. Tail heterocercal. Fins 

 membranous, each supported by a spine. Two dorsal fins, one anal fin, two pectoral fins, 

 and two ventral fins. Mouth large. Teeth conical.] 



The genus Diplacanthus comprises a greater number of species 

 than any other Acanthodean genus, at the same time it does not 

 appear to have been nearly so numerous in individuals as the 

 allied genus Cheimcanthus. Professor Agassiz has described four 

 species, viz., Diplacanthus striatus from Cromartie, Diplacanthus 

 striatulus from Lethen, Diplacanthus longispinus from both the 

 above-mentioned localities, and Diplacanthus crassispinus from 

 Caithness and Orkney. To these Professor M'Coy has added two 

 species from the latter locality, viz., Diplacanthus gihhus and 

 Diplacanthus perarmatus. The newly-discovered ichthyolitic 

 deposit of Farnell has supplied a seventh species, which I proceed 

 to describe. 



Description. — The only specimen I have yet seen of this species 

 belongs to the Eev. Henry Brewster of Farnell, and was forwarded 

 to me with many other interesting specimens by Mr. Powrie 

 of Keswallie, Forfar. It is in excellent preservation with the 

 exception of the extremity of the tail, which is wanting. It 

 measures four inches in length by three-quarters of an inch in 

 depth. Were the specimen entire, it would probably be half an 

 inch longer. On comparing these dimensions with those of the 

 other species, it appears that the proportion of the depth to the 

 length is considerably less in the species under consideration. 

 Diplacanthus striatulus is in this respect most like Dipdacanthus 



