490 
ACTINOPTERYGII. 
The end of the tail of an undetermined species of HemirJiynchus 
has also been described as follows :— 
Homorhynclius hruxelliensis, P. J. Van Beneden, Bull. Aead. Boy. 
Belg. [2] vol. XXXV, (1873), p. 210, with plate. Palceo- 
rhynchum hruxelliense^ H. Le Hon, Prelim. Mem. Poiss. 
Tert. 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. Premaxillae produced into 
an elongated rostrum and fused together towards their anterior 
extremity; dentition feeble or absent. Vertebrae 24 to 26 in 
number, about half being caudal .; the centra firmly united, and the 
neural and baemal spines expanded into laminae. Pectoral fins of 
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 with 2 or 3 rays.; dorsal fin much elevated, 
undivided ; scales present .. Ilistiojyhoriis. 
Rostrum rounded in section; teeth minute, persistent; 
pelvic fins a single spine; dorsal fin not deeper than 
trunk, divided in adult; scales present .., Tetrapturus, 
Rostrum much depressed, a flattened blade; teeth absent 
in adult; pelvic fins absent; dorsal fin much elev^ated, 
usually divided in adult; scales absent in adult.. . . Xiphias. 
The known fossils are too imperfect to be referred with certainty 
to their respective genera. Most of them probably belong to 
Histiojpliorus or Tatrajptuvus but at least one genus from the 
Eocene is distinguished from the existing members of the family 
by the form of the cranial roof and the duplication of each nutritive 
canal in the premaxillae {Xiphiorhynchus). 
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. 
