468 Mr. E. L. Gill on an undescribed Fish 



in the angular displaced bone lying on the upper part of the 

 preoperculum. A group of small plates immediately above 

 the maxilla presumably represent some of the circurporbitals. 

 Overlying them anteriorly is a prominent, roughly triangular 

 bone, which possibly also belongs to the circumorbital series 

 in the position of a lachrymal. A large curved plate lying 

 in the region of the orbit may be the displaced pterotic 

 (''squamosal'^) ; its true outline is largely concealed. Near 

 the front of the snout is a conspicuous lateral pit, presumably 

 for the nasal sac ; its outer wall was either unossified 

 or has broken away. Most of the opercular apparatus is 

 missing on this side. Behind and above the back of the 

 maxilla is a large bone, which I take to be the preoper- 

 culum ; from a small ventral end it widens greatly upwards 

 and is curved forwards. A strap-shaped anterior border 

 with obscure tubercles is marked ofiP from the hinder and 

 upper portion, which is slightly tumid and transversely ridged. 

 The only other elements of the opercular apparatus which 

 appear are two of the smaller branchiostegal rays lying 

 below the infraclavicle. 



The shoulder-girdle is almost completely displayed on 

 the left side. The uppermost element, the post-temporal, is 

 proportionately larger even than in most Palseoniscids. Its 

 hinder border is probably not quite complete. The bone 

 is ornamented with concentric ridges parallel to the margins, 

 the ridges nearest the median line being tuberculated. 

 The supraclavicle (supracleithrum) is a similar bone to the 

 post-temporal, and of about the same size. As seen in the 

 specimen it is apparently displaced upwards and forwards ; 

 in life the shoulder-girdle would have the same wide arch as 

 the back of the head, but in this nodule it has been flattened 

 laterally like the body behind it, and the component bones 

 have had to adjust themselves to the unnatural position. 

 The cleithrum (^' clavicle '^) is of unusual size. Its most 

 conspicuous portion is a strong ridge running downwards 

 and backwards from the supraclavicle, then bending slightly 

 forwards and expanding into three adjacent ridges which 

 may have reached nearly to the ventral margin. It is 

 probably this ridged portion of the cleithrum which appeared 

 at the surface behind the opercular plates. Both in front 

 of it and behind it there are considerable expansions of the 

 bone. The anterior of these expansions is deep-seated, and 

 may have formed a sort of basin as in the sturgeon. The 

 posterior expansion may in part represent one or more post- 

 clavicular scales, but it is likely that most of it was overlaid 



