490 
ACTINOPTERIGII. 
The end of the tail of an undetermined species of Hemirhynchus 
has also been described as follows : — 
HomorhyncJius bruxelliensis, P. J. Van Beneden, Bull. Acad. Roy. 
Bolg. [2] vol. xxxv. (1873), p. 210, with plate. Palceo- 
rliynchum bruxelliense, H. Le Hon, Prelim. Mem. Poiss. 
'I’ert. Belg. (1871), p. 14 (name only). — Middle Eocene 
(Bruxellian) ; Brussels. 
Family XIPHIIDiE. 
Trunk fusiform, with much-contracted caudal pedicle and large, 
forked caudal fin ; skeleton very robust. Premaxillee produced into 
an elongated rostrum and fused together towards their anterior 
extremity ; dentition feeble or absent. Vertebras 24 to 26 
number, about half being caudal; the centra firmly united, and the 
neural and hmmal spines expanded into laminae. Pectoral fins ot 
moderate size; pelvic fins with less than 5 articulated rays, or 
entirely absent ; dorsal fin much extended, with few anterior spines, 
a small posterior portion sometimes separated; anal fin also ex- 
tended, sometimes with small separate posterior portion. Squama- 
tion more or less discontinuous or absent. Air-bladder large. 
“ Sword-fishes ” are common in all tropical and subtropical seas, 
and three genera are distinguished as follows 
Rostrum rounded in section; teeth minute, persistent ; 
pelvic fins witli 2 or 6 rays ; dorsal fin much elevated, 
undivided ; scales present iristiophorus- 
Rostrum rounded in section ; teeth minute, persistent ; 
pelvic fins a single spine; dorsal fin not deeper than 
trunk, divided in adult ; scales present Tetvciptm * 1 *' 
Rostrum much depressed, a flattened blade; teeth absent 
in adult; pelvic tins absent; dorsal tin much elevated, 
usually divided in adult; scales absent in adult X iphias. 
The know'n fossils are too imperfect to be referred with certain') 
to their respective genera. Most of them probably belong to 
1 fistiophorus or Tetrapturus ; but at least ono gonus from the 
Eocene is distinguished from tho existing members of the faroil) 
by the form of tho cranial roof and tho duplication of each nutritive 
canal in the premaxillas ( Xiph ioi hynch as). 
Genus XIPHIORHYNCHUS, Van Beneden. 
[Bull. Acad. Roy. Belg. (2) vol. xxxi. 1871, p. 499.] 
Syn. (?) Ommatolampes, G. Fischer de Waldheim, Ommatolampes et 
Trachelacanthus, 1851, p. 4. 
