NATURAL HISTORY SOCIETY OF GLASGOW. 87 



Apophyses, rather large for the size of the plate--, semicircular and 

 plain, dying off towards the sides. On the interior the plate is 

 divided into two almost equal portions by the ridge separating the 

 face from the imbricated position ; the facets are large and placed 

 on each side of the central line. Posterior plate semi-capuliform, 

 convex ; apex blunt, placed at the end of the dorsal ridge in the 

 middle line, but not projecting beyond the posterior margin, from 

 whence the same declines rapidly and abruptly to the posterior 

 margin of the plate-surface, diagonally angulate on each side to the 

 lateral margin, dividing the plate into its three areas ; from the 

 apex forwards the central line is ridge-like. Posterior margin 

 semicircular in outline ; anterior margin gently convex throughout 

 its whole course, or sometimes slightly concave in the middle. The 

 ornamentation of the surface in all these plates is upon the same 

 plan ; regularly and closely set granules arranged in concentric 

 lines, larger and more apparent round the margin, but faintly 

 present over and around the apical region, where the concentric 

 character also becomes in a measure lost, but an occasional impressed 

 concentric line is present. On the intermediate plates the concen- 

 tric lines are rather square at the lateral angles, and the granules 

 much closer on the lateral areas. 



Obs. — I have combined in one description, and under one name, 

 the three forms of plates just noticed, believing them, from their 

 general appearance and ornament, to be the remains of one form. 



There is undoubtedly a very close analogy between these plates 

 and those described under the name of C. Loftusianus by Prof. W. 

 King,* and more in detail by my friend, Mr. J. W. Kirkby,f from 

 the Permian rocks of Northumberland. The difference between the 

 two forms chiefly consists in the form of the posterior plate, and the 

 apophyses of attachment ; the broader anterior plate ; the absence 

 of sulci on the dorsal areas of the intermediate plates ; and the 

 generally coarser granulation. 



It is difficult to believe, at first sight,, that the series of inter- 

 mediate plates (Plate I., figs. 2-8), figured as those of the present 

 species, are all identical. Notwithstanding, however, the difference 

 in outline shown in the figures, I do net see my way to separate 

 them, with the material at present to hand. The ornament in all 



* Perm. Foss. of England, 1851, p. 202, t. 16, f. 9-14. 

 t Quart. Jour. Geol. Soc, xviii. p. 611, t. 16, f. 31-41. 



