280 Dr. K. H. Traquair on the Structure 



be a " nuchal " or " supratemporal "*. Descending obliquely 

 downwards and a little forwards from the extremity of the great 

 supraclavicular is a very strong and well-marked clavicle (cl). 

 The vertical or principal part of the bone is elongated, and 

 greatly curved forwards in a somewhat sickle-shaped manner ; 

 it is narrow and pointed above, but expands as it proceeds 

 downwards, and at its broad lower extremity becomes sud- 

 denly bent inwards at an angle towards the ventral middle 

 line, the portion internal to the flexure being, however, very 

 short. Attached to the front of the expanded lower extremity 

 of the clavicle is still another element, a small interclavicular 

 (i.cl), like that of Paltsoniscus, though much less developed. 



Conclusion. — As regards the description of the scales, fins, 

 and internal skeleton, I have nothing of consequence to add 

 to what has been already done by Dr. Young. The new 

 facts brought out in this paper regarding the structure of the 

 head, however, render a revision of the generic characters of 

 the fish necessary. They may be summed up as follows : — 



Family Platysomidse. 



Subfamily Amphicentmnje. 



Genus Amphicentrum. 



Form deep and rhombic; dorsal and ventral margins elevated 

 into peaks ; tail heterocercal, deeply cleft, nearly equilobate. 

 Dorsal and anal fins with elongated bases, many-rayed, nearly 

 equal, commencing immediately behind the dorsal and ventral 

 peaks, their anterior margins furnished with well-developed 

 fulcra ; ventrals not discovered ; shoulder-girdle provided with 

 interclaviculars. Scales very high and narrow, and in nearly 

 vertical bands (except on the body-prolongation in the upper 

 caudal lobe, where they are small and acutely lozenge-shaped) ; 

 lepidopleura very strong, exposed area of external surface tuber- 

 culated or striated. Pramiaxilla, maxilla, and dentary bone of 

 mandible edentulous, sharp-edged; palatopterygoid and splenial 

 bone of mandible furnished with ridges, on which occur small 

 tubercular tooth-like elevations, a patch of small tubercular gra- 

 nulations, like minute obtuse teeth, occurring also on the palate. 

 Suspensorium nearly vertical, slightly inclined forwards. 



Two species are known : — A. granulosum, Huxley, from 

 the Coal-measures of North Staffordshire and Lanarkshire ; 

 A. striatum j Hancock and Atthey, from Northumberland. 



* I use the terra " supratemporal " here in the original sense in which 

 it was employed by Bakker, Cuvier, Stanuius, &c. 



