280 
ARTHRODIRA. 
being separated in front by a small narrow pineal plate ( p .), which, 
exhibits a deep pit on its under surface for the reception of the 
pineal body. Still further forward the shield terminates in a 
small, short, and broad ethmoidal plate (<?.), of which the hinder 
border meets both the preorbitals and the pineal. A large bone on 
the cheek (fig. 42, moc.) sends forward a narrow process beneath 
the eye, and is interpreted by Pander as suborbital, by Traquair as 
maxilla, probably both in part with justification. A small element 
between this and the ethmoid is named premaxilla (pmx.) by Tra¬ 
quair, and seems to form the lower border of the narial opening (n.); 
while posterior to the so-called maxilla is a deep triangular element 
(x.) with free hinder border, not improbably to be regarded as the 
operculum. Within the orbit traces of a delicate ossified sclerotic 
ring, apparently continuous, are sometimes observable. The chon- 
droeranium is entirely unknown, but in an allied genus, Chelyo- 
pliorus , the parachordal cartilages are ossified, and there seem to be 
distinct exoccipitals ; while in a single example of Coccosteus from 
Gamrie there is distinct evidence of two pairs of bones on the 
palate bearing conical teeth. There is also a single bone in each 
ramus of the lower jaw, bearing conical teeth in its middle portion, 
the two rami meeting loosely and denticulated on the anterior 
margin at the symphysis ; but the supposed premaxilhe and maxillae 
are toothless. 
The line of separation between the cranial and abdominal armour 
forms a prominent cleft; and immediately in advance of the ventro¬ 
lateral plates of the trunk is a pair of clavicle-shaped elements, 
meeting in the middle line ventrally and termed inter-laterals 
(fig. 43by Traquair. An elongated, transversely arched median 
dorsal plate (fig. 42, m.d.) oovers the back, and is supported upon 
the neural arches of the endoskeletal axis beneath by a longitudinal 
ridge on its attached surface. ' Tour flattened plates, two above and 
two below, cover the anterior part of each side of the abdominal 
region, these being termed anterior and posterior dorso-laterals 
(a.cl.l. and p.cl.l .), anterior and posterior laterals ( a.l . and p.l.). 
The anterior dorso-lateral exhibits a small rounded process on its 
front margin, to constitute a firm but readily movable joint with 
the exoccipital bone of the cranial shield; while the antero-lateral 
plate meets the inter-lateral and, with it, serves to connect the 
ventral with the lateral and dorsal armour. The ventral shield 
extends as far backward as the great dorsal plate, and consists of 
two principal pairs of elements, the anterior and posterior ventro- 
laherais (fig. 43, a.v.l. and p.v.l .), with a small, deeply-overlapped, 
diamond-shaped median ventral (vi.v.),. and a somewhat larger 
anterior median ventral ( a.m.v .). 
