HYBODUS. 5 



trunk of Hyhodiis basaniis from the Wealdeii of the Isle of Wight and Sussex 

 show still better the shape of the jaws and branchial arches, besides the usual 

 notochordal axial skeleton of the trunk, and the supports of the two dorsal fins. 



Hi/hodiis hasanus is the only Wealden species sufficiently well known for 

 definition. The other Wealden and Purbeck species are represented by isolated 

 teeth and spines, which bear merely provisional names. 



]. Hybodus basanus, Egerton. Plate I, figs. 1, 2; Plate IT, fig. 1; Text- 

 figures 3 — 5. 



1845. Hyhndus basanus, P. M. Gr. Egerton, Quart. Journ. Geol. Soc, vol. i, p. 197, pi. iv. 

 1889. Hijhodiis basanus, A. S. WooclwarJ, C.ital. Foss. Fishes B.>M., pt. i, p. 273, pi. xii, figs. 

 1891. Hybodus basanus, A. S. Woodward, Proc. Yorks. Greol. Polyt. Sac, vol. xii, p. <6i, pi. i; pi. ii, 

 fio". 1 . 



s. 1-5. 



Fig. 2.—Hijhodus havffianus, Fraas; restoration of skeleton, about one-fifteentli nat. size.— Upper Lias; 



Holzmaden, Wiirtemberg. 



Type.- — Imperfect skull and mandible with dentition; Museum of Practical 

 Geology, Jermyn Street, London. 



Specific Characters.— Teeth with a very high, much compressed crown ; median 

 cone, narrow, slender, slightly arched inwards; lateral cones two, sometimes with 

 a rudiment of a third, short l)ut sharply pointed ; coronal surface marked by 

 numerous very fine vertical wrinkles, often extending to the apices of the lateral 

 cones, but always absent on the smooth upper portion of the median cone. Dorsal 

 fin-spines rather slender and not much arched, laterally compressed, with a sharp 

 anterior keel ; lateral face of exserted portion completely covered with sharp but 

 fine longitudinal ridges, about eight being widely spaced, and those near the 

 posterior border closely arranged ; inserted base slender and tapering, its anterior 

 border sometimes inclined at an angle to that of the exserted portion. A single 

 pair of large postorbital cephalic spines with a terminal l)arb. Conical dermal 

 granules small and fluted. 



Description of Specimens.— The type specimen is an imperfect skull and 



