SCOMBEIBiE. 
453 
Genus ISURICHTHYS, nom. nov. 
Syn. Isurus^ L. Agassiz {non Rafinesque, 1810), Poiss. Foss. vol. v. pt. i. 
1844, p. 51. 
Trunk deeply fusiform, the much-contracted caudal pedicle 
apparently without hony keel. Teeth probably minute. Vertebrae 
about 30 in number, the centra much constricted, apparently with 
two lateral pits separated by a longitudinal ridge; all haemal arches 
simple. Paired fins apparently small; dorsal fins scarcely separated, 
the anterior consisting of about 8 to 10 spines; posterior dorsal 
and anal fins considerably extended, perhaps without finlets; 
caudal fin deeply forked. [Scales unknown.] 
Isairichthys macrurus (Agassiz). 
1837. Isurus macrurus, Sir P. Egerton, Catal. Foss. Fish (name 
only). 
1842-44. Isurus maci'urus, L. Agassiz, Poiss. Foss. vol. v. pt. i. p. 51, 
pi. xxi. figs. 3, 4. 
1886. Isurus macrurus, A. Wettstein, Fischfauna Tertiaer. Glamer- 
schief. (Denkschr. schweiz. Palaeont. Ges. vol. xiii.), p. 90, pi. vii. 
figs. 1-6. 
Type. Imperfect fish; British Museum. 
The type species, attaining a length of about 0*15. Proportions 
uncertain, but length of head with opercular apparatus probably 
about equalling maximum depth of trunk and one third total length 
of fish to base of caudal fin. Vertebrae 12 in the abdominal, 16 in 
the caudal region. Anterior dorsal fin consisting of 8 spines, 
posterior dorsal of 16 to 18 well-spaced articulated rays; anal fin 
with 15 or 16 articulated rays. 
All known specimens are imperfect and considerably distorted. 
Form. ^ Log. Oligocene: Canton Glarus, Switzerland. 
P. 453, P. 3999. Type specimen, in counterpart, described and 
figured by Agassiz, loc. dt .; Engi. 
Egerton EnnisTeillen Colls. 
36088. Larger, obliquely-distorted specimen, in counterpart; 
Plattenberg. Purchased, 1861. 
41820. Well-preserved caudal region ; Engi. Purchased, 1869. 
Isurichthys orientalis, sp. nov. 
Type. Nearly complete fish; British Museum. 
Apparently a smaller and more slender species than the type. 
