286 
ACTLNOPTERYGII. 
Caudal pleurocentra and hypocentra 
never annular 5 marginal teeth large, 
splenial teeth much smaller and 
mostly in single series ; dorsal fin in 
advance of anal; caudal fin forked : 
scales smooth or delicately pectinated, 
deeply overlapping . 
Ditto, but dorsal fin opposed to anal .... 
Caudal pleurocentra and hypocentra in 
form of alternating complete rings; 
^ t dentary teeth large, maxillary and 
splenial teeth much smaller and in 
a single close series; dorsal fin in 
advance of anal; caudal fin forked; 
scales deeply overlapping. 
II. Vertebral ossifications in the form of solid 
discs. 
External bones much ornamented and 
cranial roof without elevations; 
marginal teeth large and regular; 
scales thick, with feeble peg-and- 
socket articulation, not deepened on 
the flank, very narrow ventrally .... 
III. Vertebral ossifications uncertain, but pro¬ 
bably rings. 
Much resembling Neorhombolepis, but dif¬ 
fering especially in the development 
of a pair of elevations on the cranial 
roof immediately behind the eyes . . 
Cciturus (p. 329). 
Callopterus (p. 351). 
Eurycormus (p. 352). 
Neorhombolepis (p. 355). 
Lophiostomus (p. 358). 
Genus EUGNATHUS, Agassiz. 
[Poiss. Eoss. vol., ii. pt. ii. 1844, p. 97. x ] 
Syn. Lissolepis, J. W. Davis, Ann. Mag. Nat. Hist. [5] vol. xiii. 1884, 
p. 448. /I let, /&/£ ( ) • 
Isopholis, K. A. von Zittel, Handb. Palaeont. vol. iii. 1887, 
p. 216. 
Trunk elongate-fusiform. External bones feebly ornamented 
with tuberculations or rugae ; teeth relatively large and spaced on 
the dentary, smaller and more closely arranged on the margin of 
the upper jaw, minute and almost granular on the inner bones, in 
1 The name Eugnathus appears to have been first quoted, but without 
definition, by Sir P. Egerton, London & Edinb. Phil. Mag. [3] vol. viii. 1836, 
p. 368. 
