[MATTHEW] STUDIES ON CAMBRIAN FAUNAS 63 



St. John, N.B. But when we consider the species, it appears that the 

 Upper Paradoxides beds species is not this one, but one which according 

 to Mr. Walcott is found 2,000 feet lower down in the Cambrian succession 

 of the Eocky Mountains, in company with Olenellus. It may be inferred 

 thus that the genus lived on through the intermediate time, and that the 

 Mount Stephen species is a later development of the type. 



Bathyuriscus. — There remains one genus of the Mount Stephen 

 fauna which has i-elatives in the Upper Paradoxides beds. This is 

 Bathyuriscus, and they are connections which at first sight seem rather 

 distant. If, however, we strip from Anomocare limbatum, its flattened 

 borders, the remainder of the test will be a not inapt representation of 

 Bathyuriscus. A condensation of such expanded borders is in some 

 genera a mark of the adult stage, and in others is a mark of develop- 

 ment in the later species. It may be suggested then that the Anomocare 

 phylum has given rise to Bathyuriscus, and that the latter belongs to a 

 later fauna than the former. 



Neolenus, Zacanthoides and Ory otocephalus. — We come now to speak 

 of a group of trilobites of the Mount Stephen fauna, which are more 

 difficult to deal with. They have one feature in common, however, 

 which is of some significance, namely, the sharp backward angulation of 

 the pleurtT? outside the pleural groove, an angulation which ajiplies to the 

 thorax as well as the pj-gidium. So far as I recollect, no species with 

 this type of pleura are found in the Paradoxides beds ; they firtst appear 

 in the Olenus Fauna, and are a marked feature of the Peltura fauna, as 

 may be seen in Parabolina, Parabolinella and Sphairophthalmus. This 

 would indicate the Peltura fauna as the home of such genera as those 

 named at the head of this paragraph. But the Mount Stephen genera 

 differ notably in two respects from those of the Peltura Fauna of the 

 north of Europe ; in the first place their eye-lobes are set much further 

 back, and in the second they have much fewer joints in the thorax. The 

 advanced and condensed eye- lobe is a mark of high development in Cam- 

 brian trilobites ; but on the contrary, numerous joints in the thorax at 

 the expense of the pygidium is a feature of low organization ; it marks 

 the Lower Cambrian as compared with the Upper Cambrian and Ordo- 

 vician trilobites. We can only suppose that these two groups of 

 trilobites with backward-angulated pleurae, originated from the same 

 root stock in different areas, and had an independent development. So 

 far as evidence of structure goes they may have been contemporary. 



Ogygia. — This is essentially an Ordovician type, and to find it in 

 such a fauna as that of Mount Stephen is something of a surprise. The 

 species is not strictly typical of Ogygia, and the points in which it differs 

 (as the eye-lobe less arched, and more distant from the glabella) may 

 indicate an earlier form of the genus, and one which is actually Cambrian. 



Summing up the points brought forward in this review of the 



