CEPHALASPII)^. 



55 



specimen, and shows very little of the surface, fig. G, PI. XII, which shows so much more, 

 may be taken as more fiiirly representing it, and was so regarded by Dr. llarley. 



The character of the tubercles varies on different parts of the same shield in this 

 species very greatly ; in some parts there are fewer tubercles than others, and they are 

 round and of equal size ; in other parts they are crowded so as to leave no intertubercular 

 surface, and are small and large, oval and round, and irregular. This latter arrangement 

 is seen near the margin more particularly, which, as we saw in Scaphaspis (PI. I, fig. 4 a), 

 is subject to crowding and irregularity. 



The remarkable scutes drawn in PI. VIII, figs. 2 and 3, present a very large form of 

 ornament, which is regular in size and hemispherical, as seen in PI. VIII, fig. 4. They 

 occm-red in association with the specimen drawn in fig. 2, PL XII, and, no doubt, belong 

 to the same species of fish, the character of their substance and ornament leaving little 

 room for doubt on this point. It is the occurrence of these very remarkable scutes which 

 has induced me to form the subgenus Zenaspis, since they indicate an arrangement of the 

 armature of the body quite different from that of C. Lyellii. The scutes are symmetrical in 

 form, and were therefore probably placed in the median line, probably on the dorsal 

 surface. In PI. XIII, figs. 17 and 18, somewhat similar and smaller scutes are drawn. 

 These additional scutes, which thus characterise the subgenus Zenaxjih. a])parently belonged 

 to bigger individuals than that drawn in PI. XII, fig. G, for which tlk ir ornament is too 

 large. All fragments of such additiomd plates as these should be carefully looked after 

 by collectors, shice the specimens figured, and others less definite which have been sub- 

 mitted to me, indicate a considerable development of such plates, in the place of the 

 scales of Eitcephalaspis, and may possibly require a generic in place of a subgeneric 

 recognition. The flank-scales of individuals as large as Mr. Lee's specimen must have 

 been of considerable strength and size, if they retained merely the relative proportions 

 seen in Eucephalaspis ; but if, as is not imj)ossible, they united in parts to form still 

 larger plates, we may expect assuredly that they should be detected in the Corn- 

 stones. 



The ' rims ' of the cephalic shield of this species arc sometimes found alone, being 

 solid and of a shape to resist destruction after the breaking away of the expanded dome 

 which carries the orbits, &:c., as may be observed in other species (see PI, IX, fig. 4, 

 and PI. XIII, fig. 19). 



8. Cephalaspis Lightbodii. PI. XIII, fig. 19. 

 Name. — After Mr. Lightbody, of Ludlow. 



Stratigraphical Positioti. — Tilestones, near Ludlow ; from the same fine argillaceous 

 bed which furnishes Hemicyclaspis Murchisoni and Auchetiaspis Salteri. 



Characters. — The peculiar form of ornament definitely characterises this species. On 



