STLTJRID^. 
331 
occipital, extending backwards to meet a nuchal plate. Cleft of 
mouth small, not extending beneath the orbit; teeth minute, 
villiform 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 fin far forwards, in advance of the 
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 exjisting species of this genus are both marine and fresh¬ 
water, and range throughout the tropics of both hemispheres. 
Arms egertoni (Dixon). 
[Text-figure 11.] 
1850. Silurus egertoni, F. Dixon, Geol. Sussex, pp. 112, 204, pi. xi. 
figs. 11-13. 
1887. Arius egertoni, A. S. Woodward, Geol. Mag. [3] vol. iv. p. 304, 
figs. 1, 2. 
1889. Arius egertoni, E. T. Newton, Proc. Zool. Soc. p. 206. 
1889. Arius egertoni, L. Dollo, Bull. Soc. Beige Geol. vol. hi. 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 long, 
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. Log. Middle Eocene : Sussex; Belgium. 
25612. Type specimen, the clavicle and pectoral spine, figured by 
Dixon and described by the present writer, loc. cit.; 
Bracklesham Beds, Bracklesham Bay. The spine measures 
about 0’09 in length. Diocon Coll. 
25735*, 25736. Imperfect dorsal and pectoral spines, figured by 
Dixon, op. cit.p\. xi. figs. 12, 13; Bracklesham. 
Bixon Coll. 
25735, 25737, 25741. Portions of pectoral and dorsal fin-spines, 
and two ornamented head-bones ; Bracklesham. 
Bixon Coll. 
