1906.] THE SKULL OF A YOUXG RIBBOX-FLSH. 549 



The Angidare (ang.) is a very small bone on the inner suiface 

 of the infi"a-meckelian part of the articulare. It does not meet the 

 dentary as the angulare of H. glesne does, 



B. The Suspensorium and Hyoid Arch. 



The Quadrate has the usual triangular shape with a curved base 

 directed backwards ; the apex, which is directed forwards, not 

 downwards as in ordinary fish-skulls, articulates with the articulare 

 at the level of Meckel's cartilage. 



The Ectopterygoid (PI. XXXYIII. figs. 1 & 2) is a smaU trian- 

 gular bone lying in a nearly vertical plane. At its lower end the 

 bone is pointed and gradually widens to its upper border, where it 

 meets the palatine. The posterior margin fits on to the anterior 

 upper margin of the quadrate, and the dorsal border continues the 

 curve of that bone (PI. XXXIX. fig. 7), Relatively it is a short 

 bone compared Avith that of R. glesne, in which it projects for a 

 considerable distance — almost half its total length — beyond the 

 quadrate. 



Behind the Ectopterygoid lie the Ento- and the Metapterygoid, 

 extending below the orbit and curving in towards the middle line. 

 The entopterygoid stretches from the posterior border of the 

 palatine, pteiygoid, and quadrate anteriorly to the hyoman- 

 dibular posteriorly ; only the upper mai'gin is ossified, a consider- 

 able amount of cartilage still existing along the lower border. 

 The metapterygoid is a very smaU ossification of oblong shape 

 lying below the hinder end of the entopterygoid. In R. glesne 

 the latter is a somevv^hat quadrate bone about as high as it is 

 long. In the present species the great length and relatively small 

 vertical height of this bone f oi'm a marked contrast, as it extends 

 beyond the metapterygoid nearly to the hyomandibular, whereas 

 in R. glesne the bone does not reach the hinder end of the meta- 

 pterygoid. The metapterygoid, too, is longer and narrower, 

 relatively, than in R. glesne, and wholly undei'lies the ento- 

 pterygoid. 



Above the pterygoid lies the Palatine, a V-shaped bone with 

 the sharp apex directed forwards. The two Kmbs embrace the 

 end of the mesopterygoid. Although this bone in R. glesne is 

 very irregular, there is little indication of this deep notch. 



The Hyomandibular articulates with the cranium just behind 

 the orbit and below the pterotic. At this end it is broad and 

 thick, but narrows to a point as it passes downwards and forwards. 

 This narrow portion lies on the inside of the pterygoid plate. 

 The articular end is capped by cartilage, and under this is a 

 convex articulation for the opercular bone. 



At its anterior, pointed, end the hyomandibular is connected 

 with the Symplectic, which extends to the quadrate, thus con- 

 necting it with the hyomandibular. In shape the sjonplectic is a 

 long rod-like bone, slightly curved and much more elongated than 

 that of R. glesne. 



