64 
WELLBURN : OX THE GENUS MEGALICHTHYS, AGASSIZ. 
the different species, being in M. Hibherti Agassiz about a third 
the greatest length. The anterior angle is pointed, the others 
.somewhat blunt. A specimen in the Author's Collection shows 
on the upper edge of the bone, and a short distance from the 
anterior extremity, a short, blunt projection, similar to the one 
mentioned by Dr. Traquair on the maxilla of Bhizodojjsis (op. 
cit., p. 172). (PL XIX., Fig. A.) 
The pre-maxillne are separated by a median suture, and form 
the lower and anterior boundary of the cranial shield. When 
seen from the palatal surface the bone is spatulate, with a rounded 
fore edge. 
The mandible is of a very complex structure, but the com- 
ponent parts are, in the older fishes, firmly united together. 
Behind there is a distinctly ossified articular element. The upper 
and outer border, in front of the angular bone (Ag), is formed 
by an elongated element (D), the dentary bone, wdiich is deep 
and thick at the symphysis, but from this point it gradually 
tapers backwards to a fine point. Its lower border is bounded 
by a series of three plate-like, lenticular bones, which form a 
series in front of the angular element (Ag), and are termed infra 
dentaries. The inner w^all of the ramus is formed by a thin 
sphenial lamina, and between this and the dentary is a series of 
three or four stout lenticular bones, the laniaries. (PI. XVIII. 
mt^ PI. XIX., Fig. B.) 
Dentition. — Tipper. The pre-maxilkie and vomerine bones 
bear within and close to either outer extremity a large tooth, 
and on each side of the middle line in front is a similarly 
socketed large tooth. The small marginal teeth are continuous 
with two curved rows of equally small teeth which pass in front 
of the outer tusks, and curving inw^ards, meet in the middle line 
anterior to the basilar bar, whose surface is closely set with fine 
denticles.'"" Behind, on either side, are two palatine bones, which 
seem to be wedged in between the maxillae and pterygoid bones. 
Each plate bears a marginal row of short, stout, conical teeth, 
Young, op. cit,, p. 605. 
