SILURID-R. 
: J31 
occipital extending backwards to meet a nuchal plate. Cleft of 
roouth small, not extending beneath the orbit ; teeth minute, 
v 'llif'orm or granular, extending over the vomer and palatines. 
Pectoral fins with a robust spine, serrated on one or both borders ; 
Pelvic fins with six rays ; dorsal tin far forwards, in advance of tho 
pelvic pair, with one robust spine and six or seven divided rays ; 
adipose fin short-based or of moderate extent ; anal fin short-based ; 
caudal fin forked. Skin naked. 
The existing species of this genus are both marine and fresh- 
water, and range throughout the tropics of both hemispheres. 
Arius egertoni (Dixon). 
[Text-figure 11.] 
1800. Silurus egertoni, F. Dixon, Geol. Sussex, pp. 11-, 204, pi. xi. 
figs. 11-13. 
1887. Arius egertoni, A. S. Woodward. Cieol. Mag. [3] vol. iv. p. 304, 
figs- 1, 2 . 
1889. Arius egertoni, E. T. Newton, Proc. Zool. Soc. p. 206. 
1880. Arius egertoni, L. Dollo, Bull. Soc. Beige Geol. vol. iii. Proc.- 
Verb. p. 218. 
type- Pectoral arch and spine ; British Museum. 
A small species known only by fragments. External ornamen- 
tation of bony plates consisting of sharp conical tubercles, frequently 
united at the base by low and rounded reticulating ridges. Poste- 
rior extension of supraoccipital bone slightly broader than lon B , 
with nearly parallel sides, truncated hinder border, and a longitudinal 
keel ; the anterior half of this bone marked with a pair of con- 
spicuous grooves for the slime-canals diverging forwards from the 
median keel. Pectoral fin-spine compressed, with irregular longi- 
tudinal ridges, partly tuberculated, and with both borders serrated : 
post-clavicular plate triangular, as deep as long. 
Form. Lo C . Middle Eocene : Sussex; Belgium. 
25612. Type specimon, the clavicle and pectoral spine, figured by 
Dixon and described by the present writer, loc. at.; 
Bracklesham Beds, Bracklesham Bay. f he spine measures 
about 0-09 in length. ColL 
25735 *, 25736. Imperfect dorsal and pectoral spines, figured by 
Dixon, op. cit. pi. xi. figs. 12, 13 ; Bracklesham. 
1 ' Dixon Coll. 
25735. 25737, 25741. Portions of pectoral and dorsal fin-spines, 
and two ornamented head-bones ; Bracklesham. 
Dixon Coll. 
