lO (î. F. MATTIIEAV ON THE 



Except the doubtful graptolites ol' Vermont ' uo fauua ol' the deeper and colder 

 waters appears in association with Oleuellus.' lu most cases the Oleuelhis fauua followed 

 ou saudstoues often of great thickness, and quite barren of fossils ; the species are found 

 in green and grey mud beds intercalated in the sandstones or in thin limestone layers, 

 seldom or never in the black mud frequented by the later species of the genus Para- 

 dox ides. 



So many Cambrian sections in the interior of America are now known, from which 

 Paradoxides is absent, that we may suppose it never invaded that region, and that it sup- 

 planted Olenellus in Scandinavia and on the Atlantic coast of America owing to the 

 sinking of the land in these parts, and the influx of sea-water of a different (colder ?) 

 temperature. If such was the case we can easily understand that the genus Olenellus 

 may have existed in the interior bays and sounds of America, long after it was driven 

 from the Atlantic shore by the invading Paradoxides fauna. . 



Through the west and south of North America the Olenellus beds were succeeded by 

 limestones, which probably indicates a continuance of warm seas in those regions, and 

 there no Paradoxides have been found. 



These peculiarities of the deposits which contain respectively Olenellus and Para- 

 doxides lead us to contemplate the probable co-existence of the two genera in different 

 areas. But if we are right in attributing to Paradoxides a greater tendency to a pelagic 

 habit than Olenellus, it is clear that the former will almost invariably be found to overlie 

 the latter when they successively occupied the same area. 



VI. — DiCELLOCEPHALUS — DiCTYONEMA.'* 



The two parts of the Cambrian system which contain black slates are separated in 

 Acadia as in "Wales by flags and shallow-water beds. These beds by their fossils do not 

 exhibit a return to the earlier faunas, but the known trilobites (genus Oleuus) are the 

 natural predecessors of Parabolina, etc., of the upper black beds ; this would seem to 

 indicate the continuance of cold seas. In Sweden the member is not marked by shallow- 

 water beds, bnt has a succession of Alum slates containing several species of Olenus ; 

 in that country there seems to have been uo elevation of the sea-bottom when the Oleni 

 flourished as there was in Wales and Eastern Canada. This stage of the Cambrian corres- 

 ponds to the Sillery sandstone of the St. Lawrence valley, and also probably to the typical 

 Potsdam sandstone of the state of New York. 



One of the most characteristic genera of this period in America was Dicellocephalus. 

 The genus appears to have had its centre of dispersion in the region of the Upper Missis- 

 sippi, for there it exhibits the greatest variety of species, and the species become less 

 numerous as we recede from this region, east and west.' 



Eastward of the "Wisconsin localities the Potsdam fauna with Dicellocephalus is met 



' Doubtful as regards the genus. 



"It is in accordance with this that the Archieocyathids are plentiful in Sardinia, while they appear to be 

 wanting in the Olenellus beds of Russia. 



•' The Dictyonenaa referred to in this paper is D-flabdliforniC. 



* The Wisconsin species are D. Minnesolend.i and D. Pepinendu, Owen, and D. misa, D. «jmugtr and D. Osceola, 

 Hall. 



