254 



SCIENCE. 



[N. S. Vol. V. No. 111. 



The author proposed, with Matthew, to 

 regard the Etcheminian series and its equiv- 

 alents as Pre-Cambrian, but still Paleo- 

 zoic ; and, as suggested by himself many 

 years ago, to classify the Huronian and 

 Grenvillian as Eozoic, leaving the term Arch- 

 aean to be applied to the Lower Laurentian 

 gneiss, until it also shall have afiforded 

 some indications of the presence of life. 



He insisted on the duty of paleontolo- 

 gists to give more attention to the Pre- 

 Cambrian rocks, in the hope of discovering 

 connecting links with the Cambrian, and 

 of finding the oceanic members of the 

 Huronian, and less metamorphosed equiva- 

 lents of the Upper Laurentian, and so o^ 

 reaching backward to the actual beginning 

 of life on our planet, should this prove to 

 be attainable. 



An extremely interesting paper by Dr. 

 Matthew dealing with a kindred subject 

 and entitled 'Some Features of the early 

 Cambrian Faunas.' 



The paper referred chiefly to the larval 

 features of the early Cambrian Trilobites, 

 because in them we may look for points of 

 structure which will appear in the adult 

 condition of their predecessors. But allu- 

 sion was also made to the early Cambrian 

 Brachiopoda and Ostracoda. 



Trilobites. — Except in Olenellus and its al- 

 lies the larval forms of the earliest trilobites 

 are little known, but in those of the Para- 

 doxides beds a number of series of the 

 larval forms are known belonging to differ- 

 ent genera, so that in these we have fuller 

 data for comparison. 



Cambrian time has been called the ' Age 

 of Trilobites,' and their abundance and va- 

 riety is truly remarkable. The flexibility 

 of the type is indicated by the numerous 

 genera that appeared successively in that 

 early age. They thus become valuable in 

 marking the divisions of the Cambrian rocks 

 as the vertebrates do those of the Tertiary. 



The utility of their remains is manifest in 



the ease and certainty with which different 

 parts of the Cambrian System can be recog- 

 nized in all the regions around the Atlantic 

 Ocean, where rocks of this age have been 

 found. This being the case, it may be prof- 

 itable to examine the forms of the earliest 

 Cambrian trilobites and note how they com- 

 pare with the larvse of those of the Para- 

 doxides beds. The law of development would 

 lead us to expect that in the pre-Paradoxides 

 faunas of the Cambrian certain features of 

 the larval forms of the trilobites of the Par- 

 adoxides beds should appear as permanent 

 adult features in their predecessors. Let us 

 see if such is the case. 



In 1892 Dr. J. Bergeron summed up the 

 evidence on this point, derivable from the 

 trilobites of the Paradoxides and Olenellus 

 faunas in his article ' Is the Primordial the 

 most Ancient Fauna?'* He used the studies 

 of Barrande, Walcott, Ford and others for 

 this purpose, and his conclusion was that 

 there must have been a more ancient fauna. 



Discoveries of other faunas beside that of 

 Olenellus have been made since Bergeron 

 wrote upon this subject, and we may now 

 place his theory against some additional 

 facts which bear upon it. 



To make the application clearer some of 

 the characteristics of the earliest larval 

 stages of the trilobites of the Paradoxides 

 beds as shown in the young of Paradoxides, 

 Ptychoparia, Conocoryphe, Microdiscus and Ag- 

 Tiosiws may be presented. Among them are 

 the following: 



1 . Predominance of the cephalic over the 

 caudal shield. 



2. A long, narrow glabella, with nearly 

 parallel sides. In these early moults the 

 posterior lobes of the axial rachis (which 

 includes the glabella) are short and weak 

 compared with the anterior and especially 

 the first.f 



* Revue generale des sciences, Paris, 1892. 

 t Paradoxides is apparently an exception to this 

 rule, but we do not know its earliest stages. 



