CIMOLICHTHYS. 43 



Description of Specimens. — The type specimen in the Dixon Collection com- 

 prises an imperfect mass of scntes, of which those best preserved are still arranged 

 in regular series and exposed fi*om the inner aspect. The latter are shown upside 

 down in Dixon's original figure ; and one of the associated fragments displaying 

 the outer face is similarly inverted. The only other specimens hitherto discovered 

 are scattered scutes. 



All these scutes are very deep and narrow, and crossed near their upper end by 

 the canal of the lateral line. When complete each scute is six or seven times as 

 deep as broad ; and it exhibits a slight sigmoidal curvature, the sharpest bend 

 being forwards above the lateral line. Each end co-ntracts to a blunt point, the 

 posterior border converging to the anterior border at the upper extremity (PL IX, 

 figs. 5, G, 9), while the reverse convergence occurs at the lower extremity (Dixon's 

 figure and PL IX, figs. 7, 8). The anterior border of the scute is bevelled to a very 

 slight extent for the overlapping of the preceding scute; and there is a little 

 vertical ridge on the smooth inner face marking the hinder limit of the overlapping 

 facette at least in the lower part of the scute (fig. 4, v.). A broad band at the 

 hinder margin of the outer face is covered with a regular series of strong and 

 parallel pectinations, which are inclined somewhat obliquely downwards and back- 

 wards- and end in sharp points. The piercing canal of the lateral line (figs. 5, 6, 

 9, /.) forms a prominent smooth ridge, which is rounded and widest in front but 

 tapers to an acute spine behind. Below this ridge the anterior half of the outer 

 face of the scute is almost or quite smooth, with not more than feeble traces of 

 vertically disposed rugae. Above the lateral line the outer face behind the pectina- 

 tions is marked with one or more sharp vertical ridges. 



Horizons and Localities. — Zone of Ilolaster siiljglobosus : Burwell and Cherry 

 Hinton, Cambridgeshire; Dover; Clayton, Sussex; Calne, Wiltshire. Zone of 

 Holaster planus : Swaffham, Norfolk. 



Fragments of scutes of Prionolepis, much like those of the type species but 

 completely covered Avith a conspicuous rugose ornament, are also knoAvn from the 

 Chalk of Dorking, Surrey (Capron Collection, B. M. no. 49776). 



.Gen as CIMOLICHTHYS, Leidy. 



Cimolichthys, J. Leidy, Trans. Amer. Phil. Soc, vol. xi, 1857, p. 95. 

 (?) Plinthojjhorns, A. Giiuther, G-eol. Mag., vol. i, 1864, p. 115. 

 Empo, E. D. Cope, Proc. Amer. Phil. Soc, vol. xii, 1872, p. 347. 



Generic Characters. — Head elongate and acutely pointed; trunk elongate- 

 fusiform. Cranial roof exhibiting a deep median longitudinal depression, its 

 lateral and occipital margins ornamented, like some of the other external bones, 



