CHIR0CEXTRIDJ5. 
99 
the caudal fin. Teeth smooth, stout, and nearly circular in trans- 
verse section, those of the mandible slightly larger than those of 
the upper jaw ; oral border of maxilla nearly straight, that of the 
dentary feebly sinuous. Vertebral centra as deep as long, about 
25 in the abdominal, 35 in the caudal region. Dorsal fin opposite 
the middle of tlio anal fin, which comprises somewhat more than 
30 rays, the foremost seven or eight closely adpressed and forming 
the lobe. 
The unique original specimen of this species in the Geneva 
Museum is preserved in counterpart ; and although there is a 
fracture across the unusually short abdominal region, it does not. 
appear to have lost any intervening portion. The skull is im- 
perfect behind, but is shown to have been wide between the orbits, 
with a very robust prefrontal (ectethmoidal) ossification. The 
premaxilla is not preserved ; and neither the fossil nor its counter- 
part now exhibits the anterior upper tooth-bearing fragment of 
bone represented in Pictet’s figure. The characteristic maxilla is 
distinct, fractured across its anterior half and not intelligibly 
shown in the figure. The sinuous contour of the oral border of 
the mandible is also exaggerated in the latter ; and the fossil is 
not sufficiently well preserved to determine whether or not the 
mandible really tapers to the symphysis so much as appearances 
suggest. There are remains of thin cheek-plates ; and one pre- 
operculum is displaced beneath the opercular region. A few traces 
of delicate branchiostegal rays occur below the mandible. The 
so-called anterior dorsal fin of Pictet is a false appearance due to 
the displacement of some neural spines, where the squamation has 
also been disturbed (as noted by Bassani, loc. cit.). 
Form, if Lor,. Neocomian : Yoirons, Geneva, Switzerland. 
Not represented in the Collection. 
Genus ICHTHYODECTES, Cope. 
[Proc. Amer. Phil. Soc. vol. xi. 1871, p. 53G.] 
Syn. Gillicus, O. P. Hay, Amer. Journ. Sci. [4] vol. vi. 1898, p. 230. 
Teeth hollow, in deep sockets, not compressed to a sharp edge ; 
those of the maxilla, as also those of the dentary, almost uniform 
in size, and those of the premaxilla not much enlarged. Succes- 
sional teeth formed directly beneath the functional teeth, and no 
nutritive foramina on the inner face of the jaw below the alveolar 
border. No presymphysial bone. Vertebral axis, fins, and scales 
apparently ns in Chirocentrites. 
h 2 
