BOTHRIOLEPIS MAJOR. 115 



description resolves itself therefore more or less into an explanation of the plates. 

 Most of these figures represent plaster casts taken from sharp impressions 

 occurring in a hard, siliceous, vitreous-looking, coarse, sometimes even pebbly, sand- 

 stone at Carden Hill, Sweet Hillock, and Rocky Park, near Alves, and in this 

 way the details of the external form and sculpture are brought out in a manner 

 which could not be attained by figuring the fossils themselves. 



Head. — PI. XXIII, Fig. 1, shows a head, natural size, and perfect except as 

 regards the extra-lateral and angular plates, which are wanting. To be noted is the 

 course of the sensory groove, and its comparative nearness to the margin of the head 

 in front ; also the V-shaped commissure on the median occipital and lateral plates, 

 the orbit being set between the limbs of the V. Another head is shown in 

 Fig. 5, with parts of the anterior median dorsal and anterior dorso-lateral 

 plates in apposition behind, and in this specimen the sculpture is finer and the 

 tubercles in many places run together into tolerably straight lines, while in other 

 places an irregularly reticulated pattern is formed. 



In Fig. 2 of the same plate we have the median occipital plate of a large indi- 

 vidual, natural size, showing the deep indentation in front for the post-median 

 element, behind which is the posterior commissure of the sensory groove. The 

 pre-median element is shown, natural size, in Fig. 3, crossed in front by the 

 sensory groove which in the middle is flexed into a sharp angle with backwardly 

 directed apex. A portion of the right lateral plate is also represented of the 

 natural size in Fig. 4, showing the sensory groove with its antero-lateral branch. 

 This must have belonged to a large specimen, and it may be noted that the 

 sculpture is proportionately large and coarse. 



Body. — In Fig. 1 of PL XXIV is shown, one half natural size, a plaster cast of 

 an anterior median dorsal plate. Its form is broad, depressed, gently convex, but 

 not heeled ; hexagonal, but the anterior margin has nearly twice the extent of 

 the posterior. At the posterior margin is seen the transversely elongated 

 triangular area overlapped by the posterior median dorsal, but the lateral areas 

 overlapped by the posterior dorso-lateral plates are not visible. The nature of the 

 external sculpture needs no description. Another anterior median dorsal plate 

 (cast) is shown, natural size, in PL XXIII, Fig. 6, the coarse external sculpture 

 of which is to be noted. Although the plate is exactly one half the linear size of 

 the one last described, the tubercles, ridges, and intervening hollows are just as 

 large, and in like manner very considerably larger than those on the corresponding- 

 element in Fig. 5, which when complete must have had about the same dimensions. 



In PL XXIV, Fig. 2, we have a photograph one half natural size, of the 

 internal surface of a similar plate taken from an actual specimen from Newton 

 Quarry, Alves. Here is distinctly shown the median ridge extending from nearly 

 the posterior margin right on to the front, while about one third from its anterior 



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