186 
S. WATSON AND MR. E. L. GILL ON THE 
muscle, forms the "hatchet-shape" which Hancock and. Atthey attributed 
to this bone. 
Apart from the much greater strength of the bones in Sagenodus, the 
points of difference between its shoulder-girdle and tliat of Ceratodus are 
insignificant (fig. 19, p. 185). The strong forward process of the post- 
temporal in Sagenodus is plainly associated with the presence of a tabular 
horn, to which it was doubtless attached by its truncated point. In 
Ceratodus the post-temporal is merely attached to cartilage. The process of 
the cleithrum which serves to stiffen the union with the clavicle is repre- 
sented in Ceratodus by a pyramidal point (tig. 19,- p.), which if the bones 
■were flattened would lie in the middle of the internal face instead of on the 
hinder border. In Ceratodus the muscle-pit in the head of the clavicle is 
divided by ridges into two or three pockets, but some of the clavicles of 
Siigenodus show an approach to the same condition. Finally, there can 
be no doubt that the blade of the clavicle was twisted as it is in Ceratodus, 
so that what appear in the flattened bones (fig. 19, A, B, p. 185) as its upper 
Fi&. 20, 
Sagenodus. Restoration of skull and shoulder-girdle, in side view, x |. cor., two of the 
ciroumorbitals ; vm.t., vomerine " tooth." Each bone is founded on specimens in the 
Atthey Collection, but the association of the ciroumorbitals is conjectural. 
and lower edges were in life the inner and outer edges respectively ; while 
the surface represented in fig. 17, E, p. 182, and fig. 19, A, p. 185, is really 
the upper and internal surface, and that represented in fig. 17, F, and 
fig. 19, B, the lower and external. This will be understood from a comparison 
between the outline drawings in fig. 19, where the middle figures, C and D, 
show the shoulder-girdle of Ceratodus as it would appear if it were flattened 
out, like the bones of Sagenodus, by fossilization in shale. The actual 
specimens of the cluviule of Sagenodus show abundant evidence of having 
been strongly curved, for the flattening has produced a system of gaping 
cracks on the smooth inner face of the bones (fig. 17, G, p. 182). One 
