178 
TEOF. D. M. S. WATSON AND MK. E. L. GILL ON THE 
rolling of the upper and lower borders very markedly. The " dentaries " are 
even more variable than the other bones of the jaw, both as regards shape 
and surface chara.cter. Three different patterns are shown in fig. 15, p. 180. 
Tlie " dentary " there marked C is one of the shortest in relative length and 
deepest at the symphysis ; some are even narrower than the one figured at A. 
The symphysis itself is coiiinionly of the character shown in D, much like 
that of the " splenial " in fact ; but a quite different type occurs in which 
the " dentaries " were united by interlocking spines, as shown at A. The 
Sagenodua. Reconstruction of lower jaw, X i. A, doreal, R, ventral, C, lateral, 
D, medial aspects; E, "splenial," from the outer side; F, angular, from the mesial 
side ; ang., angular ; " &«,," " dentary " ( = splenial) ; sp., splenial ( = pre-articular) 
(Compare with figs. 13 of Ceratodus and 27 of Ctenodus.) E is S. imbricatas; the 
rest of the figures S. obliquus. The deep symphysis of E can be matched in the 
latter species. 
line of sensory pits in the angular is often continued on the "dentary," and 
where this is the case one of the pits seems regularly to lie on the suture 
(fig. 14, p. 180). Near the. posterior border of the " dentary " there is 
often a row of tliree or four much smaller pits. In some pairs of 
"dentaries" the posterior borders would apparently meet across the middle 
line in an even curve ; in others these borders are strongly hooked at the 
