200 
ACTINOPTERYGII. 
depth of the trunk nearly equal to the length of the head and trunk 
without caudal hn ; distance from frontal angulation to hinder margin 
of preoperculum equalling about one-quarter of the total length of 
the fish. [Dentition imperfectly known, but] teeth smooth, some 
indented, and those of the principal mandibular series at least twice 
as broad as long. Dorsal and anal fins equally elevated, the latter 
with about 30 rays and four-fifths as long as the former, which has 35 
ra}^s. Squamation covering less than half of the trunk; ridge-scales 
coarsely serrated, each on the ventral aspect with about six points. 
It seems probable that the so-called Mescdon gibbosus 1 is founded 
upon a small, distorted fish of this species. The original specimen 
is in the Palaeontological Museum, Munich, and was obtained from 
the Lithographic Stone of Kelheim. Three other small fishes from 
Eichstadt, in the same Museum, also probably the young of 
M. macropterus,Y>Q&T the name of M. pulchellus (A. Wagner, loc. cit. 
vol. ix. 1862, p. 351). Another dwarf variety, from the Middle 
Purbeck of Teffont, Wiltshire, is named M. macropttrus, var .parvus 
(A. S. Woodward, Geol. Mag. [4] vol. ii. 1895, p. 147, pi. vii. 
fig. 2). 
Form. <$)' Loc. Lower Kimmeridgian (Lithographic Stone) : 
Bavaria. 
P. 5546. W^ell-preserved fish 0*14 in length, shown of two-thirds the 
natural size in PI. XYI. fig. 1; Eichstadt. As shown in 
side view, the basicranial axis is bent sharply downwards 
at the front of the orbit (o.) to the dentigerous vomer (v.); 
and some of the sutures in the cranial roof can be dis¬ 
tinguished. The limits of the supraoccipital ( s.occ .), 
squamosal ( sq .), and parietal (pa.) plates are quite clear, 
and the latter element bears a large process (x) on its 
hinder margin, this directed backwards and subdivided 
into digitations at the extremity. The operculum (op.) 
and preoperculum (p.op.) are imperfect, but their relative 
proportions and characteristic radiating markings are seen. 
Some of the long hour-glass-shaped basals (b.) in the 
pectoral fin can also be observed. There are no scales on 
the caudal region, and the endoskeleton is thus well 
exposed. By exchange , 1888. 
1 A. Wagner, Abk. k. bay. Akacl. Wiss., math.-pliys. Cl. vol. vi. (1851), 
pp. 52, 56, pi. iii. fig. 2. Gyrodus gibbosus, L. Agassiz, Poiss. Foss. vol. ii. pt. ii. 
1844, p. 236 (name only, ex Munster, MS.). A distorted specimen of Mesodon 
from the Lithographic Stone of Cirin, Am, France, is also described under the 
same specific name by Y. Thiolliere, Poiss. Foss. Bugey, pt. ii. (1873), p. 13, 
pi. ii. fig. 12. 
