68 WEALDEN AND PURBECK FOSSIL FISHES. 



Description of Specimens. — This species is known only by the splenial hone, 

 of which the anterior part bears teeth like those of Athrodon. The normal 

 dentition does not begin until the bone has attained a width of at least a centi- 

 metre. The type specimen (PI. XV, fig. 12) exhibits the short and broad bone 

 with a wide inner border free from teeth. The irregular teeth occupy more than 

 half of its length, but the hinder teeth are almost exactly those of Gcelodus mantelli. 

 All are much worn except the two teeth most posteriorly, which are not crimped 

 round the shallow apical pit. In part of a smaller specimen (PI. XV, fig. 13) the 

 teeth are extremely worn by mastication, and the principal teeth are inclined at a 

 considerable angle to those of the outer series. 



Horizon and Localities. — Wealden : Sevenoaks, Kent ; Battle, Sussex ; Brook 

 and Atherfield, Isle of "Wiffht. 



3. Ccelodus hirudo (Agassiz). Plate XV, figs. 14—18. 



1839. Acrochi* hirudo, L. Agassiz, Poiss. Foss., vol. iii, p. 148, pi. xxii, fig. 27. 



1887. „ ., A. S. Woodward, Geol. Mag. [3], vol. iv, p. 102. 



1889. „ ., A. S. Woodward, Catal. Foss. Fishes B. M., pt. i, p. 296, pi. xiii, fig. 9. 



Type. — Much worn tooth; British Museum. 



Specific Characters. — A species known only by isolated dental crowns which 

 sometimes attain a length of 2 - 5 cm. in longest diameter, but are usually smaller. 

 Principal teeth slightly more than twice as broad as long ; coronal contour gently 

 rounded, somewhat raised near each lateral end, and the surface marked by very 

 fine wrinkles diverging or radiating from an extended apical pit which is reduced 

 to an inconspicuous groove. 



Description of Specimens. — The type specimen, which was misunderstood by 

 Agassiz, is shown from the upper, anterior, and lateral aspects in PI. XV, figs. 14, 

 14a, b, and may be regarded as a principal tooth of the left splenial bone. It is 

 imperfect at the outer and posterior borders, and its upper surface (fig. 14) has 

 been removed by mastication, which has produced a deep hollow in the outer half. 

 The posterior broken edge shows that the main part of the tooth consists only of a 

 comparatively thin crown, without any root. The anterior face (fig. 14 a), which 

 is described and figured by Agassiz as the top of the crown, retains the charac- 

 teristic ornament of very fine vertical wrinkles. Concentric lines of growth are 

 conspicuous round the base of the crown, which is shown to have been fixed to the 

 bone by a peripheral root in the usual Pycnodont manner. 



A smaller tooth evidently of the same type was described and figured loc. cit. 



1889, displaying the shape and ornament of the unworn crown; and another good 



pecimen of intermediate size is shown in PI. XV, figs. 15, 15 a, b. Here the oral 



surface (fig. 15) is only slightly worn, so that the original contour of the tooth is 



