76 WEALDEN AND PURBECK FOSSIL FISHES. 



caudal. Principal scales smooth and somewhat concave externally, with a finely 

 serrated hinder border ; some scales irregularly punctated or rugose. 



Description of Specimens. — The type specimen, which is very imperfectly shown 

 in the original figure published by Agassiz, is re-drawn of the natural size in 

 PI. XVI, fig. 13. The outline of the head is indicated, and there are traces of the 

 coarse ornamentation, but the details of its osteology arc obscure. The shape of 

 the trunk is also clearly shown, and the fins are not very imperfect. There are no 

 indications of fulcra on the pectoral fins, but they are distinct on the pelvic fins ; 

 both basal and fringing fulcra are also seen on the dorsal fin, and they are 

 conspicuous on the upper lobe of the caudal fin. The anal fin is comparatively 

 small and deep, with eight or nine rays. The comparatively stout caudal fin-rays 

 are well enamelled. The scales are exposed chiefly from the inner face, and 

 exhibit the variations in shape already described in 0. breviceps (p. 75). Some 

 of the scales in the abdominal region exhibit their fine serration, while a few on 

 the caudal pedicle are covered with faintly rugose enamel. The lateral line in the 

 abdominal region traverses the ninth or tenth row above the ventral border. 

 , .'. The type specimen is described by Agassiz as from the Inferior Oolite of 

 Northampton, but the matrix appears to be Purbeck Stone, and a second example 

 of the same species in the British Museum was certainly obtained from the Purbeck 

 Beds of Swanage. In this specimen a few of the scales below the middle of the 

 dorsal fin, and just in front of the pelvic fins, exhibit the faint rugosity of the 

 enamel already noted on the caudal pedicle of the type. There is another example 

 from Swanage in the Museum of Practical Geology, London. 



Horizon and Localiti/. — Middle Purbeck Beds : Swanage, Dorset. 



Genus HISTIONOTUS, Egerton. 

 Histionohis, P. M. G. Egerton, Ann. Mag. Nat. Hist, [2], vol. xiii, 1854, p. 434. 



Generic Characters. — Head large, snout acute; dorsal margin of trunk rising 

 above the head to an angulation from which the body gradually tapers backwards. 

 Styliform marginal teeth very slender and closely arranged. Slime-canals on head 

 and preoperculum comparatively large. Notochord surrounded by ring-vertebrae ; 

 ribs ossified. Fins consisting of distally bifurcating rays, all with A-shaped fulcra; 

 pectoral fins much larger than the pelvic pair; dorsal fin arising at the angulation 

 of the back, extending to the caudal pedicle, high in front, low behind ; anal fin 

 small ; caudal fin forked. Scales covering the whole of the trunk, in regular series, 

 united by peg-and-socket articulation, and more or less pectinated at the hinder 

 border; scales of middle of flank and some of dorsal region deeper than broad, the 

 flank-scales with more or less convex hinder border ; ventral scales at least as broad 

 as deep; postclavicular scales very large ; caudal ridge-scales not much enlarged. 



