THE 
GEOLOGICAL MAGAZINE. 
NEW. SERIES:, .DBGADE Ill.,.VOL.. VI. 
No. VI.—JUNE, 1889. 
@ie a GIN PAS ae ee ao Cae So 
J.—Ow a New Specimen or Hisrionorus anGuLaris, Egerton. 
By J. C. Mansuu-Preypewn, F.L.S., F.G.S. 
(PLATE VIL.) 
ESTION OTUS ANGULARIS, was first described and figured 
by the late Sir Philip de M. Grey Egerton, Bart. F.R.S., in 
Decade viii. of the Memoirs of the Geological Survey, 1853. The 
uninterrupted dorsal fin, extending from near the occiput to the tail, 
suggested the generic name of HWistionotus,' and in this feature it re- 
resembles Ophiopsis. It has the characters also of other genera, for 
instance, Pholidophorus in its scales, Semionotus in the shape of its body, 
and Lepidotus in the shape of its head. Sir Philip Egerton, misled by 
the imperfect preservation of the posterior end of his specimen, 
thought the caudal-fin to be also similar to that of Lepidotus. By a 
singular coincidence, a fine specimen of Lepidotus minor lies side by 
side on the same slab with the subject of this note (PI. VII.), and the 
caudal fin of each is well exposed, showing that of Zepidotus to be 
comparatively short and truncate, while that of Histionotus is deeply 
forked. In its crushed condition, the upper lobe in Histionotus is 
longer and larger than the lower lobe; but this is proved to be a 
deceptive appearance by another example of the genus I have since 
met with from the same quarry which displays the symmetry of the 
tail-fin, the lobes being beautifully shown of equal length. 
The outline of the upper portion of the body is triangular, rising 
abruptly from the snout to a distance of 20 millim. beyond the base 
of the occiput along the dorsal ridge, and then descending by a less 
abrupt gradient from this culminating point to the base of the 
caudal fin, a distance of 85 millim. The depth of the body at the 
most elevated part of the dorsal ridge to the pectoral fin is 65 mm., 
to the shoulder-girdle 83 mm. 
The anterior margin of the first ray of the dorsal fin, which is 
stouter than the others, is furnished with a series of fulcral rays. 
The remaining rays, of which there are more than twenty, 
bifurcate about half-way from the base, and the distal halves are 
again bifurcated and cleft. The pectoral fin consists of seven rays, 
of which the first is the longest and stoutest, and all are bifurcate 
1 forios, a sail, yaros, a back. 
DECADE III.—vVOL. VI.—NO. VI. 16 
