MACROSEMIIDJE. 
173 
Ophiopsis (according to the description) in the non-bifurcated 
character of all the dorsal fin-rays. It is the type of the genus and 
species Eusemius beatce , B. Yetter, Mittheil. k. mineral.-geol. Mus. 
Dresden, pt. iv. (1881), p. 51, pi. i. fig. 3. The length of the head 
with opercular apparatus considerably exceeds the maximum depth 
of the trunk and is contained little more than three-and-a-half 
times in the total length of the fish. The dorsal fin comprises about 
32 rays; and 11 free supports are described in advance of this. 
The principal flank-scales are delicately sculptured, exhibit from 4 
to 6 strong denticulations on the posterior margin, and are deeper 
than broad; there are about 44 dorso-ventral series. 
The published notices of Opliiopsis muensteri (G. von Munster, 
Neues Jahrb. 1834, p. 385 ; L. Agassiz, Poiss. Boss. vol. ii. 1844, 
pt. i. p. 292, pt. ii. p. 289; A. Wagner, Abh. k. bay. Akad. Wiss., 
math.-phys. Cl. vol. vi. 1851, p. 60) leave the systematic position of 
this species doubtful. According to Wagner’s description, the ver¬ 
tebral centra are well ossified ; according to a figure by von Zittel, 
who names the species Isopholis muensteri (Handb. Palaeont. vol. iii. 
1887, p. 216, fig. 230), the head is indistinguishable from that of 
Eucjnaihiis. The type specimen, obtained from the Lithographic 
Stone of Kelheim, Bavaria, is an elongated fish wanting the pelvic, 
dorsal, and anal fins ; it is preserved in the Palaeontological 
Museum, Munich. 
The genus Macrepistius (E. D. Cope, Journ. Acad. Nat. Sci. 
Philad. [2] vol. ix. 1894, p. 441), so far as known, appears to differ 
from Ophiopsis only in having all the teeth tumid at the apex, ex¬ 
cept those of the premaxillae and the opposing portion of the 
dentaries. The type species is M. arencitus (E. D. Cope, ibid. 
p. 441, pi. xix. fig. 2) from the Neocomian of Glen Bose, Texas, 
probably attaining a length of about 0*3. The head and opercular 
bones are ornamented with tubercles, which become confluent on 
the hinder part of the parietals. The operculum is twice as deep 
as broad and three times as large as the suboperculum. The 
dorsal fin originally comprised not less than 32 rays. The scales 
are irregularly pitted, but not serrated on the hinder margin. 
Genus HISTIONOTUS, Egerton. 
[Ann. Mag. Nat. Hist. [2] vol. xiii. 1854, p. 434.] 
Head large, snout acute; the dorsal margin of the trunk rising 
above the head to an angulation from which the body gradually 
tapers backwards. Marginal teeth much elongated, closely ar¬ 
ranged. Notochord invested with delicate ring-vertebrae. Eins 
