﻿280 ARTHROD1RA. 



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 (pmoc.) 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 

 (a?.) with free hinder border, not improbably to be regarded as the 

 operculum. Within the orbit traces of a delicate ossified sclerotio 

 ring, apparently continuous, are sometimes observable. The chon- 

 drocranium is entirely unknown, but in an allied genus, Chelyo- 

 pJwrus, 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 premaxillse 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, 43, i.l.) by Traquair. An elongated, transversely arched median 

 dorsal plate (fig. 42, m.d.) covers the back, and is supported upon 

 the neural arches of the endoskeletal axis beneath by a longitudinal 

 ridge on its attached surface. Pour flattened plates, two above and 

 two below, cover the anterior part of each side of the abdominal 

 region, these being termed anterior and posterior dorsolaterals 

 (a.cl.l. and p.d.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- 

 laterals (fig. 43, a.v.l. and p.v.l.), with a small, deeply-overlapped, 

 diamond-shaped median ventral (m.i'.), and a somewhat larger 

 anterior median ventral (a.m. v.). 



