WELLBURN : ON THE GENUS MEGALICHTHYS, AGASSIZ. 61 
forwards to a point a little behind their middle, then forwards 
and inwards for a short distance, and then nearly straight for- 
wards to meet the posterior boundary of the bones of the anterior 
division. Along the outer edge of each parietal are two smaller 
bones (P.F. and Sq.), the anterior ones being narrow, elongated 
bones which in front meet the posterior extremity of the bones 
(Fr.) of the anterior division ; from this point, where the bones 
are the broadest, the external margins run backwards to a point, 
a little in front of the centre of the parietal bones, w^here they 
join the posterior pair of bones (Sq.) by a suture which runs 
from without, inwards, and backwards. The posterior border of 
the bones (Sq.) is straight, and they are wider here than in 
front. Their outer border at first runs forwards and slightly 
outwards, then forwards, and then inwards and forwards to meet 
the external border of the anterior pair of bones (P.F.) at the 
junction of their posterior and middle thirds. 
The anterior division of the cranial shield is divisible into 
a posterior (Fr.) and an anterior moiety (C.E.). 
The posterior division is composed of two bones (Fr.), the 
Frontals, which are divided down the middle line by an irregular 
suture ; their inner sides are longer than their outer, which are 
notched to form the upper boundary of the orbit. From the 
anterior edge of this notch, where the bones are the widest, they 
gradually narrow to form an obliquely truncated anterior extremity, 
which indents the posterior border of the bones (C.E.) in front, 
the union being by a semi-lunar suture, with the convexity 
forwards. 
The anterior division (Moignon inter maxillaire Agassiz) is 
a cresentic shield which terminates the head anteriorly, and 
presents distinct indications of a division into a number of pieces, 
viz., Ethmoids (E.), Pre-frontals (P.F.), Nasals (N.), and pre-maxil- 
lary (PMx.) bones. The bones are usually firmly united, and 
form the " Compound Ethmoid." The pre-maxillary portions are 
separated by a median suture, and form the lower and anterior 
boundary of the shield. Above these in the centre is the 
