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E. J. CHAPMAN 



by a ridge or baud with the glabella, narrow body-axis with numerous or comparatively 

 numerous segments, and small, short pygidiiim. Again in the Cambrian Dikelocephalus, 

 and in Ctenopyge (Linnarsson), the pygidium is very large — thus presenting a marked 

 departure from the so-called primordial type. Other examples might be cited to prove, 

 (1) that these imaginary primordial characteristics are present in various post-primordial 

 genera, and (2) that they are not always present in primordial or Cambrian types. 



(4.) Nothing, perhaps, shows more forcibly the arbitrary, unnatural character of 

 stratigrax)hical groupings, than the collocation in recent classifications of Neseuretus, 

 Hicks, side by side with Paradoxides in the family of the Oleuidse. In all its leading 

 characters, Neseuretus is simply a Cambrian Calymene, probably the ancestral source of 

 the latter type ; but in the classifications referred to, these genera are placed in different 

 families and widely apart. To show these points in all their distinctness, viz., the close 

 agreement of Neseuretus with Calymene, and its remote relations to Paradoxides, a com- 

 parative view of their more characteristic structures is given in the following table : — 



In these recent classifications, also, we find Dikelocephalus arranged under the 

 Olenida?, whilst Arethusiua and Harpides, which agree very strikingly with Olenus in 

 their more salient characters, are placed far apart from the latter under the Proetidse, 

 evidently upon purely stratigraphical grounds. The structural relations of these genera 

 are briefly indicated in the annexed tabular view : — 



