254 ON THE PERMIAN CHITONID.E, 



1, C. ANTiQUUs, Howse, sp. (PI. XIII., figs. 15-23.) 



Calyptrcea antiqua, Howse, 1848, Catalogue Perm. 

 Foss., p. 24; King's Mon. Perm. Foss., Aj^pendix, 

 p. 247; Howse, Ann. and Mag. Nat. Hist., 2 ser., 

 vol. xix., p. 464, PL IV., figs. 16, 17. 

 Posterior j^^cite patelliform, oval, ornamented with strong ribs 

 radiating from the apex ; lines of increment evident ; apex poste- 

 riorly situated and recurved; process of insertion extending 

 round the whole margin, somewhat within the outer, but on a 

 plane with the inner surface, produced into two bluntly pointed 

 apophyses in front, and finely denticular posteriorly. Interme- 

 diate j)lcites patelliform, oval, subpentagonal, or ovate, ornamented 

 with ribs like the posterior plate, and marked with similar 

 lines of growth, apex posteriorly situate, recurved; process of 

 insertion like that of the posterior plate, with the exception of 

 the apophyses of the frontal margin, which are not developed, 

 though the same margin is somewhat produced. Anterior 2')lcite (?) 

 patelliform, almost circular, apex subcentral; in other respects 

 like the intermediate plates. 



The plates of this species vary a little in length and width ; 

 some are almost as wide as long, others much longer than wide. 

 The former probably rej^resent the more anterior plates ; the latter 

 those placed posteriorly. Some plates have the apex more 

 elevated than others ; that which is supposed to be the most an- 

 terior has it somewhat depressed. In several plates the anterior 

 slope is rather convex, in others it is straight ; posteriorly they 

 are all somewhat concave. Occasionally the ribs vary in size 

 on the same plate, some being almost twice the width of the 

 neighbouring ones ; they also differ in convexity on the same speci- 

 men; those posteriorly situate are always the most convex; in 

 some instances they bifurcate. The margin is uneven, and always 

 more or less arched posteriorly. The processes of insertion 

 are in some cases marked with faint lines, representing the ribs 

 on the exposed surface. The size of the largest (a posterior) 

 plate is a quarter of an inch, and of the smallest one-eighth. 

 The nearly uniform, together with the anomalous character of 



