472 woodward: fossil fishes of the upper lias of whitby. 
Gyrosteus mirabilis indicated by the known remains. The largest 
hyomandibular of the latter measures 0"35 m. in length, while the 
largest clavicle attains 0*57 m. in maximum height. In Chon- 
drosteus the length of the hyomandibular is contained about 
16 times, and the maximum depth of the clavicle between 8 and 
9 times in the total length of the fish. The largest individuals 
of the Whitby species thus probably attained a length of from 
5 to 6 metres. 
A smaller form probably of Gyrosteus is represented by 
some small bones in the British Museum from a comparatively 
soft stratum at an unknown horizon in the Whitby Lias 
(recorded in Catal. Foss. Fishes B. M., pt. iii., p. 42). 
Explanation of Plates. 
Plate LXVIII. 
Fig. Page. 
1. Gyrosteus mirabilis, Ag., MS. ; slab exhibiting group 
of bones, one-ninth nat. size. Ch., ceratohyal ; cL, 
clavicle ; e., external bone, tuberculated ; /., fin-rays ; 
hm., hyomandibular ; pns., parasphenoid ; s.cL, supra- 
clavicle ; x., undetermined external bone, tubercu- 
lated. [36185.] ... ... ... ... 462 
2. Gyrosteus mirabilis ; three vertebral arches, one-third 
nat. size. [P.3356m.] ... ... ... ... 468 
Plate LXIX. 
1. Gyrosteus mirabilis, Ag., MS. ; left opercular apparatus, 
inner aspect, about one-third nat. size. Br}'"^, branchi- 
ostegal rays ; op., operculum ; s.op., suboperculum. 
[P.7520.] ... ... ... ... ... 467 
The specimens represented on these plates are preserved in 
the British Museum, and the numbers in square brackets refer 
to the Register of the Department of Geology. 
