STRUCTURE OF CERTAIN PALEOZOIC DIPNOI. 
185 
temporals, again, is the parasphenoid, the backward prolongation o£ which 
is seen emerging from beneath them. The only other specimen we have 
seen showing the connection of cleithrum and clavicle is a detached example 
oE these two bones in the Royal Scottish Mnseum. 
A few remarks are called for on points of detail. As with other bones of 
the skeleton, those of the shoulder-girdle are variable, the cleithrum especially 
so. The inner face of the cleithrum is flattened ; the outer is convexly 
thickened towards the upper end, and is strengthened by ribs of bone running 
Fig. 19. 
Sagmiodus and Ceratodus. Comparison of shoulder-girdles. 
A, B. Right side of shoulder-girdle of Sagenodus. 
C, D. ,, „ „ Ceratodus, with the bones supposed 
flattened as are the fossil bones of Sagenodus. 
E, F. Right side of shoulder-girdle of Ceratodus, with the bones in natural shape. 
(Outer views on left, inner on right.) 
upwards from the junction with the clavicle. Crushing has often resulted in 
these ribs being more or less plainly printed through on to the inner face. 
The cleithrum ends below in a transverse edge which is received into the 
head of the clavicle, and its hinder border is produced into a flattened and 
pointed process which fits into a slot in the back of the clavicle. The 
expanded upper end of the clavicle, with its deep pit for the attachment of 
