OF THE SKULL IK LEPIDOSTEUS OSSEUS. 
447 
orbital ” series of small, thick ganoid scutes, which run before and behind into other 
tracts, and are not separated as a mere ring. The upper region is composed of a chain 
of larger bones than the rest, and this tract is continued forwards as three bones, 
narrowing forwards, in the preorbital region, over the “ prequadrate space/’ Behind 
and above, these larger bones run backwards under the squamosal until they become 
the “post-temporals” to which the clavicular bones are attached. They are the direct 
cephalic continuation of what in the Teleostei are known as the “ lateral line ” series. 
A row of small scutes runs straight down in front of the orbit from the preorbital 
band; the lowest of these binds on the quadrate, over the hinge, and over the foot of 
the preopercular. From this angular bone there is an increasing number of scutes 
under the orbit, and those behind the orbit become a solid tesselated pavement (part 
of which I have just described as lying directly beneath the squamosal), and this 
pavement lies on the edge of the lower part of the interopercular and covers all its 
ascending part. 
This most remarkable “ interopercular ” is much like the preopercular of the Tele - 
osteans, and might easily be mistaken for it. It is a huge plate bent upon itself at 
a right angle; the ascending part is half the size of the lower region, and whilst 
covered by the facial “ pavement,” itself covers the hyomandibular and symplectic ; that 
part is pointed above. The lower region of the bone is a large externally ganoid tract, 
pointed in front, ear-shaped behind, hollow within, and coiled inwards. Behind the 
facial pavement, and articulated by a cup-like facet to the “ opercular process ” of the 
hyomandibular, is the opercular bone; it is four-sided, but narrow above where it 
articulates with the post-temporal. Its broad lower edge is toothed and overlaps the 
subopercular; its hind face is free and forms the upper half of the free edge of the 
operculum. The “ subopercular ” forms the lower half of that edge ; it is a broad plate 
with a rounded lower and hinder margin, and is uncinate in front and above, where 
it is wedged in between the interopercular and opercular. These three bones—the 
interopercular, the opercular, and the subopercular—belong to the hyomandibular region. 
The splints of the mandible are ganoid where they are exposed. The main bone is the 
“ dentary ”; it covers nearly all the outside of the ramus and the upper and lower 
edges within. On the inside, between those edges, Meckel’s cartilage is hidden in its 
foremost two-thirds by a long, thin, narrow splint, the “ splenial.” The rami of the man¬ 
dible are close together, half-way, backwards, and then gently diverge. The coronoid 
region is very high, large, and incurved. The “ coronoid” bone flanks the front of this 
part as an oblique splint, and the “ supra-angulare ” covers the smooth, convex outside ; 
a short, thick, wedge of bone, the “ angulare,” is set on to the angle of the ramus. 
These five bones—the dentary, splenial, coronoid, supra-angulare, and angulare—are the 
normal investing bones of the mandible. In the lower part of the hyoid arch there are 
three narrow flattened rays, from an inch to am inch and a-half in length, attached to 
the outer face of the “ epi-hyal”; these are the “ branchiostegals,” and they correspond 
in number to what we find in the Cyprinoid Teleosteans. 
MDCCCLXXXII. 3 m 
