FOSSILS OF THE CAMBRIAN. 



postero-lateral angle, as Mr. Ford has pointed out for the form, fig. 1 1 , of O. 

 asaphoides, and also in the genus Paradoxides. 



Attention is again called to the direction of the facial suture back of 

 the eyes, in figs. 3 and 4, and the position and obliquity of the 1 eyes in re- 

 lation to the median line of the glabella, characters of Paradoxides, as seen 

 in P. spinosus. Of all the species of the latter genus, P. Kjerulfi* alone 

 shows the presence of an ocular ridge uniting the eye and the frontal lobe 

 of the glabella, fig. 15 (a), a feature so prominent in the young of 0. Howelli, 

 as well as the small, rounded protuberance between the eye and the glabella, 

 shown in Linnarsson's fig. 2, of P. Kjerulfi. The latter character Mr. Ford 

 discovered in the young of 0. asaphoides, and noted its resemblance to the 

 same in P. Kjerulfi. The ocular ridge, a feature in the latter that is per- 

 manent, is also present in the young of 0. Howelli, but disappears in the 

 adult, adding in this another link to the argument so admirably brought 

 forward by Mr. Ford to show the genetic relation of the two genera. 



Resume. The study of the head of Olenellus Howelli proves: 



First. That in certain individuals of this species the existence of em- 

 bryonic features continues long after the individual has reached the size at 

 which such features are usually lost in the process of development of other 

 species of the genus. 



Second. That in individuals otherwise developed equally in all respects 

 some one of them may have a characteristic feature, such as the eye or the 

 genal angle, developed to a greater or less degree than in the others, and 

 that this feature may persist even after the individual having it has passed 

 in size or other characters the stage at which it is usually lost 



Third. That the development of certain characters went on in an unequal 

 degree in the corresponding parts of the same individual, and, finally, that 

 certain features present in the younger individuals and disappearing during 

 the subsequent growth are permanent features in some species of the genus 

 Paradoxides. 



* fversigt af Kongl. Vetenskaps-Akademiens Forhandlingar, N:o. 6, Stockholm, p. 790, Tafl. 

 xvi, figs. 1, 2. 1871. 



