66 PISCES. 



Coccosteus (figs. 50 52). The cranial shield in this genus is irregu- 

 larly six-sided in shape, and the notches for the orbit (fig. 50, o.) are far 

 forwards. The arrangement of the plates as seen from above is indicated 

 in fig. 50, and the median element (p.}, pitted on its visceral aspect ap- 

 parently for the reception of the pineal body, is noteworthy. A large 

 bone on the cheek (mx.} sends forwards a narrow process beneath the 

 eye, and may be either maxilla or suborbital or both. In front it meets 

 a small toothless plate, which is perhaps a premaxilla (p.mx.} and seems 

 to bound the narial opening (n.) below. Behind, there is a triangular 



FIG. 51. 



Coccosteus decipiens; restoration of ventral shield by E. H. Traquair, about 

 one-third nat. size. L. Old Bed Sandstone ; N. Scotland, a.m.v., anterior 

 median ventral ; a.v.l., anterior ventro-lateral ; i.L, inter-lateral (? clavicle) ; 

 m.v., median ventral; p.v.l., posterior ventro-lateral. The thick lines 

 represent the exposed borders of the plates ; the thin lines indicate the 

 extent and direction of overlap. The dotted line marks the course of a 

 mucus-canal. 



element (#.), which occupies the position of an operculum. Within the 

 orbit traces of a delicate ossified sclerotic ring, apparently continuous, 

 are sometimes observable. The chondrocranium is entirely unknown, but 

 in an allied genus, Chelyophorus, the parachordal cartilages are ossified, 

 and there seem to be distinct exoccipitals. Two pairs of bones on the 

 palate bear conical teeth. The single bone in each rarnus of the man- 

 dible has similar teeth in its middle portion, and is denticulated on the 

 anterior margin where it meets its fellow of the opposite side. The 

 line of separation between the cranial and abdominal armour forms a 

 prominent cleft; and the ginglymoid articulation on each side takes 

 place between a process on the anterior dorso-lateral plate (a.d.l.) and 

 a cavity beneath the external occipital (e.o.}. Immediately in advance 



