ON THE PERMIAN CHITONID^E. 255 



the plates of this species, may cause some suspicion of their really- 

 representing a perfect series. I confess that at first I was of 

 opinion that my early specimens were all postal plates, and ex- 

 pected that further researches would bring to light the interme- 

 diate ones. It was only after making repeated investigations, 

 and when 1 had discovered additional specimens similar in form to 

 the first, that I was induced to adopt an opinion suggested by my 

 friend Mr. A. Hancock, that the specimens found comprised a per- 

 fect series,or at least included both posterior and intermediate plates. 

 In support of this opinion the number of the discovered plates 

 may be quoted. In all, ten have been found. They were ob- 

 tained from one spot — from an area of a few cubic yards. Now, 

 were we to suppose all these ten specimens to be postal plates, 

 ought we not to produce some traces of the seventy intermediate 

 and anterior plates belonging to the ten individuals from which 

 the supposed postal ones have been detached ? And on such a 

 supposition, would it not be necessary to explain the manner in 

 which so strange an assortment of plates had originated ? Such 

 an idea, however, is altogether untenable; for there exists no 

 grounds upon which to base so arbitrary an assumption.* There 

 are no data to show how so large a number of posterior plates 

 could be gathered together without the intermixture of others. 

 In short, there is nothing to countenance this opinion; and it 

 can only be maintained by referring their occurrence to accident 

 — to some strange freak of chance altogether unexplainable. In- 

 stead, therefore, of adopting this unwarrantable conjecture, it 

 seems more in harmony with the facts of the case to adopt Mr. 

 Hancock's suggestion, and to consider the plates a mixed series. 

 In the case of Chiton Lqflmlanus, and of all other species of Per- 

 mian Chitonidce, the intermediate plates were always the first to 

 occur. These jDlates, of course, also comprise the major portion 

 of the discovered remains of each species ; and though the plates 

 of each are always met with unarticulated, yet the different 



* It may, of coarse, be imagined tliat the plates of tliis species might be of different 

 gi-avities, or fixed in the mantle with different degrees of tenacity, so tliat they might be 

 distributed over an area in sorts by a current of a certain strength acting upon the habitat 

 of the species; but, as stated in the text, there is no proof of this— rather the converse. 



