246 ON THE PERMIAN CHITONIDJE. 



greater number of the plates found, however, must have belonged 

 to much smaller specimens — some of them apparently to indi- 

 viduals not much longer than half-an-inch; but, as the largest 

 plates may not be of maximum size, the species may have 

 exceeded somewhat the above measurement. 



In arranging the plates of this species in the sequence in 

 which they are figured, I have been guided by the arrangement 

 observed in those of many recent Chitons, such as C. Cumingii, 

 C. sulcatus, C. cinereus, C. magnijicus. With the exception of the 

 second plate, the intermediate plates of these species vary little 

 in length and general form, though the central ones are the 

 widest j the second plate is much longer than these, and is easily 

 distinguishable from them. The intermediate plates of (7. Lof- 

 tusianus resemble those of the recent species just mentioned. 

 The greater number of those that occur are short and more or 

 less transverse; a few are much longer, and not so transverse. 

 From the more frequent occurrence of the former, it must be 

 evident that a predominance of such plates characterised this 

 species ;* and, from their similarity of form to those of many 

 recent species, it is but analogical to suppose that their mode of 

 arrangement was after the same plan. 



Mr. Howse is of opinion that the order of the plates was not 

 after this fashion, but that the general form of the species was 

 ovate, or " much narrower in front than behind." f In arrang- 

 ing the plates, he places as his second one of the intermediate 

 plates of Chiton cordatus, and as his third the second of the pre- 

 ceding description ; he also makes a difference between his third 

 and fourth ; so that on the whole his restored Chiton is a very 

 different one from mine. It is perhaps more in accordance with 

 our knowledge of the recent Chitons to consider that the pecu- 

 liar plate which Mr. Howse has placed as the second belongs to 

 a distinct species, rather than to a form the rest of whose plates 

 do not appear to have any affinity with it and which compose a 



* Out of ninety-one plates which I have obtained at Tunstall Hill, sixty-three belong to 

 the short, transverse type, and fourteen to the more elongate form ; the remainder are 

 posterior and anterior plates. 



t Mr. Howse considers that it closely approached some of the recent spinose species, such 

 as C. spinulosus, from the great length of its anterior plates. 



