ALBULIDiE. 
67 
Mouth terminal, the mandible with truncated symphysis and high 
coronoid region ; a single series of small, conical marginal teeth ; 
stouter and blunter teeth within the mouth, but apparently not on 
the parasphenoid. About 10 branchiostegal rays. Vertebral about 
90 to 100 in total number, the centra short and deep, marked with 
delicate longitudinal ridges. Pelvic fins scarcely smaller than the 
pectorals, which are inserted high on the flank ; dorsal fin extending 
for more than half of the back ; anal fin short, opposed to or behind 
file posterior end of the dorsal ; caudal fin deeply forked. Scales 
elliptical, not pectinated. 
Ihe existing deep-sea genus Bathythrissa (A. Gunther, Ann. 
Mag. Nat. Hist. [4] vol. xx. 1877, p. 443) or Pterothrissus (P. Hil- 
gendorf, Leopoldina, pt. xiii. 1877, p. 127), is not yet clearly dis- 
iiuguiBhed from Istieus. For description and figure, see A. Gunther, 
Pep. Deep-Sea Fishes, ‘ Challenger ’ Report, Zool. vol. xxii. (1887), 
P- 222, pi. Ivi. fig. a. 
Istieus grandis, Agassiz. 
1842-44. Istieus grandis, L. Agassiz, Poiss. Foss. vol. v. pt. i. p. 13, 
pt. ii. p. 92, pi. xviii. 
1842-44. Istieus microcephalus, L. Agassiz, ibid. pt. i. p. 13, pt. ii. 
P- 94, pi. xvii. [Imperfect fish ; Palaeontological Museum, 
Munich.] 
1842-44. Istieus macrocephalus, L. Agassiz, ibid. pi. xvi. lower fig. 
(err ore). 
1858. Istieus grandis, W. von der Marck, Zeitschr. deutsch. geol. Ges. 
vol. x. p. 246. 
1858. Istieus microcephalus, W. von der Marck, ibid. vol. x. p. 246. 
1803. Istieus macrococlius, W. von der Marck, Palreontogr. vol. xi. 
p. 37, pi. iv. figs. 1-5. [New name for I. grandis + I. micro- 
cephalus . ] 
1863. Istieus mesospondylus, W. von der Marck, ibid. vol. xi. p. 38, 
pl. v. fig. 1. 
1863. Istieus macrocephalus, W. von der Marck, ibid. vol. xi. p. 39, 
pl. iv. fig. 6, pl. v. fig. 3 ( errore ). 
1873. Istieus macrocoelius, W. von der Marck, ibid. vol. xxii. p. 59, 
pl. ii. fig. 2. 
1885. Istieus macrocoelius, W. von der Marck, ibid. vol. xxxi. p. 253. 
Type. Imperfect fish; Paris Museum of Natural History. 
Ihe type species, attaining a length of about 0-0. Length of 
ead with opercular apparatus contained about two and a quarter 
tlmos > maximum depth of trunk about three times in the length 
fl '°m the clavicle to the base of the caudal fin ; width of caudal 
p 2 
