468 woodward: fossil fishes of the upper lias of whitby. 
Gyrosteus differs from the sturgeon but agrees with Chondrosteus 
in the presence of an extensive branchiostegal apparatus. 
The vertebral axis is practically unknown, but one fragment 
in the British Museum (No. P.3356?72) seems to exhibit five of 
the neural or hremal arches without their appended spines. 
•Fig. 10. — Left clavicle of recent Fig. 9. — Gyrosteus mirahilis, Ag., 
sturgeon (^ajoe;i.ser), outer MS.; left clavicle, outer aspect, 
aspect, much reduced. one-sixth nat. size. [Brit. Mus., 
No. P.3356(^.] 
These arches are in regular series, and three of them are 
shown of one-third the natural size in pi. Ixviii., fig. 2. They 
are more expanded in their basal half than the neural 
arches in Chondrosteus* and they seem to have been closely 
pressed together, without any intercalary pieces ; but the hard 
matrix obscures their precise shape. Above the basal half they 
*Cf. Catal. Foss. Fishes B. M., pt. iii., pi. i., fig. 4. 
