woodward: fossil sturgeon of the WHiTiiY LIAS. 103 



complete in the adult, small examples of the hyomandibular 

 appearing much less extended below than the one here figured. 

 Some of the parts of the hyoid arch are also bony in the Whitby fish, 

 and two elements, probably to be regarded as ceratohyals, are shown, 

 of one-third the natural size, in fig. 5. There is at least one large 

 quadrangular bone in the gill-cover, but no branch iostegal rays have 

 been observed. The gill-arches were partially-ossified rods, as in the 



Ceratohyal bones of Gyrostens luirabilis; one-third natural size. 



modern Sturgeon (fig. 8,;), these being met with as long, hour-glass- 

 shaped bones, more slender than (but otherwise not unlike) the 

 supposed ceratohyals just referred to. 



Of vertebrce there are no traces, and the notochord must thus 

 have been persistent in Gyrostens, as in all Sturgeons. There seem, 

 however, to be distinct slender ribs in a specimen in the British 

 Museum ; and Prof Blake has made known some supposed neural 

 arches. 



April 1890. 



