ON THE PERMIAN CHITONIDiE. 259 



of C. antiquus. In the latter species they never vary their posi- 

 tion, being always placed posteriorly. 



Some spine-like bodies which occurred with the remains of the 

 Chitonelli are figured with the plates of the present species. 

 They evidently belong to one of the Permian species of this group, 

 and possibly to the present — though just as likely to either of the 

 other two, as their remains were all found together. That they are 

 truly the exuvife of some of the Chitonidce seems to be proved by 

 their mode of growth, structure, and basal apophyses. The latter 

 character is most especially significant ; for it indicates that they 

 were fixed in some soft substance, after the manner of the plates of 

 this family ; consequently, as our knowledge of the fossils associated 

 with the Chitonelli i% such as warrants our saying that they do not 

 belong to them, we are almost equally warranted in referring 

 them to the Chitonelli, some of whose mantles may reasonably be 

 imagined to have been spinose, like those of several Chitons. The 

 spines in question may be described as follows : — Minute, short, 

 compressed, bluntly pointed, and comparatively thick; slightly sul- 

 cated on widest sides, inferior margin of same sides convex verti- 

 cally, and of the compressed sides deeply sinuate; point of insertion 

 divided into four obliquely truncate processes, which originate 

 within the inferior margin, and follow the same direction of 

 growth as the general surface. 



The chief reason which has induced me to assign the six plates 

 previously mentioned to one species is the angularity which charac- 

 terizes the whole series. There seems to be an analogy of form 

 between the posterior and intermediate plates that is evidently 

 specific. Other characters also imply their specific identity ; the 

 similarity of their ribs and of their processes of insertion, as well 

 as their general mode of growth, all seem indicative of this. 



Little can be said concerning the affinities of C. Hancockianus. 

 Its plates bear more resemblance to those of the recent Chitonelli 

 than those of C. antiquus ; but still they show great differences 

 from any yet discovered. The intermediate plates certainly pos- 

 sess a much greater analogy to the same plates of the recent 

 species than the patelliform plates of C. antiquus, and make a 



