66 
WELLBURN : ON THE GENUS MEGALICHTHYS, ACASSIZ. 
end is rounded, the anterior truncated. Behind the sj^mphysis 
of the mandible, and between, and partly overlapped by, the 
anterior ends of the principal jugulars, is a well-marked azygos 
plate, the medial jugular (M.J.), On each side are a series of 
well-marked lateral jugulars (L.J.), which increase in size from 
before backwards ; they run along the inner sides of the mandibular 
rami, and extend some little distance behind the posterior border 
of the principal jugulars. There are probably nine of these plates 
on each side. (PL XIV.) 
Conclusion. — (PI. XIII.) The body of Megalichthys was 
much elongated, somewhat rounded, and covered with rhomboidal 
ganoine-covered scales, arranged in sigmoidal rows, running from 
above downwards and slightly backwards. 
The head is long (about one-fifth length of body), broad, 
and depressed, all the external bones being covered with a dense 
layer of ganoine. Cranial roof is covered with well-developed 
bony plates, which form a compact shield divisible into an anterior 
and a posterior moiety. The nares are placed on each side of 
the rounded, depressed snout. The orbit is anteriorly placed, 
being at the junction of the anterior and posterior third of the 
head, and is bounded in front, below, and behind by well- 
developed bones. Behind, the cheek is covered by a series of 
loose dermal bones. The opercular bones are well marked. The 
jaws are powerful and well developed, the gape extending far 
back. There are teeth of two sizes on the jaws, the large ones 
being internal. Small, numerous, rasp-like denticular teeth were 
also present on the well-developed membrane bones of the mouth 
and on the edge of the sphenial. Between the mandibular rami 
the branchial apparatus is defended by a series of jugular plates, 
there being two principal, one median, and nine lateral plates 
on each side. The vertebral column is well developed, there 
being well-ossified ring-shaped centra, neural and haemal arclies. 
Neural spines were present, and in the posterior part of the fish 
haemal also. 
The shoulder girdle well developed ; paired fins obtusely 
obate and fulcrate, the ventral being abdominal in position. 
