ON THE PERMIAN CHITONID^. 249 



lively long for their width, which varies a little; median angu- 

 lation rather obtuse, apices not produced ; posterior margin rather 

 oblique; anterior margin slightly convex, sinuated medianly; ex- 

 tremities rounded anteriorly ; lateral areas wide, faintly marked, 

 being very slightly raised above the general surface, sometimes 

 marked with one or more grooved lines running parallel with the 

 lines of growth, which are extremely faint; processes of insertion 

 aiigulate, obliquely truncate, the upper edge projecting: the 

 second plate is a little longer than the others; it is narrow, and 

 the length is greater at the median line (which is slightly 

 arcuate) than at the extremities, owing to each margin being 

 somewhat oblique in a contrary direction, while in other pjlates 

 the extremities are almost as long as the median line. Posterior 

 plates less than half a circle, flattish posteriorly ; posterior margin 

 rounded; anterior margin straight; angulate medianly; apex 

 pointed, depressed, centrally situate; several indistinct lines radiate 

 from the apex posteriorly. 



Since the discovery of this species was noticed in 1857, four 

 additional plates have been found — three intermediate, and one 

 posterior. These have enabled me to give a more detailed de- 

 scription than that previously communicated, and have allowed me 

 to supply, without much restoration, figures of a complete series 

 of plates. The arrangement adopted is that which the general form 

 of the plates seems to indicate as the most likely; but, from the 

 few remains which have been found, it is scarcely possible to 

 speak with the same certainty as in the case of C. LoftusianuSy 

 whose plates, being numerous, afford much safer grounds for 

 inference. 



As characters distinguishing G. Howseanus from the preceding 

 species, the obtuse angulation of the intermediate plates, their 

 greater length, the faintness of the lateral areas, and the absence 

 of strong lines of growth, were noticed in a former communication. 

 To these may now be added the coarse granulation of the sur- 

 face, the less arcuate median line, the flatness of the posterior 

 plate, with the more anterior position of its apex and a marked 

 difference of its processes of insertion. The latter character forms 

 a good specific distinction, and was one upon which I greatly 



