woodward: fossil fishes of the upper lias of WHITBY. 461 
four times as long as its maximum depth ; distance between 
the orbit and occiput scarcely, if at all, exceeding the maximum 
depth of the mandible, and the angular bone of the latter, 
with long, nearly vertical hinder border, sharply rounded off 
inferiorly ; dentition powerful, the posterior laniaries widely 
spaced and especially robust ; superficial ornament consisting of 
short ruga?, the majority directed longitudinally. 
Family Chondrosteid^e. 
Gyrosteus mirabilis, Agassiz, MS. 
Plates LXVIII.-LXIX. 
1834-44. GyrostPAis mirabilis, L. Agassiz, Poiss. Foss., vol. i., 
p. 19, and vol. ii., pt. ii., p. 179 (undefined). 
1855. Sepia i7icom2)osita, M. Simpson, Foss. Yorkshire Lias, p. 21. 
1858. Gyrosteus mirabilis, P. M. G. Egerton, Phil. Trans., p. 883. 
1876. „ „ J. F. Blake, in Tate and Blake, York- 
shire Lias, p. 256, pi. ii., figs. 2, 3. 
1889-90. „ ., A. S. Woodw^ard, Proc. Geol. Assoc., 
vol. xi., p. 32, figs. 2-7 ; and The 
Naturalist, 1890, p. 101, figs. 1-6. 
1895. „ ,, A. S, Woodward, Catal. Foss. Fishes 
B. M., pt. iii., p. 34, figs. 7, 9, 10, 12- 
14, 16, 17. 
Type : Various bones ; British Museum. 
When visiting Whitby in 1834, Agassiz observed "some 
gigantic fragments of a fish which certainly surpassed in size 
all those of w^hich traces had hitherto been discovered." He 
regarded these fossils as comprising "the bones of the head, 
among others a frontal bone more than a foot in length, and 
some broken branchial arches, with fragments of fins." He 
noted the remarkable absence of teeth among the remains of 
"this marine giant," and proposed to name the fish Gyrosteus 
— doubtless in allusion to the twist in the characteristic bone 
which is identified below as hyomandibular. Subsequently he 
