420 NATURAL SCIENCE. dec. 



found ; but no country has up to the present time produced a more 

 varied fauna or a greater richness in types than England. Scandi- 

 navia has a larger number of species, but not so many groups." 

 The classes at that time represented in the Cambrian rocks of South 

 Wales were the following, viz., Spongida, Echinodermata, Annelida, 

 Brachiopoda, Gasteropoda, Pteropoda, Crustacea, Trilobita. In the 

 table, in the paper above referred to, seven classes only are men- 

 tioned ; but since then it has been shown that the genus Stenotheca, 

 which I had previously discovered in the Menevian rocks at St. 

 David's, should be classed with the Gasteropoda. 



Mr. C. D. Walcott, Director of the United States Geological 

 Survey, in his very important memoirs, " The Fauna of the Lower 

 Cambrian or Olenellus Zone," 4 and " Correlation Papers, Cambrian," 5 

 makes careful comparisons of the rocks on both sides of the Atlantic, 

 which contain the Cambrian faunas, and says that " in lithologic, 

 stratigraphic, and palaeontologic characters, the Cambrian series on 

 the opposite sides of the Atlantic are such that there is no hesitancy 

 in considering them as belonging to one geologic group and as part 

 of one geologic basin." ^ He further points out that the Lower 

 Cambrian fauna, which he regards as a littoral fauna, is much more 

 persistent in its character than that in the succeeding rocks, " for all 

 the strata referred to the former horizon have been found to be 

 characterised by essentially the same fauna." The Lower Cambrian 

 fauna in America, according to Mr. Walcott, contains genera belong- 

 ing to the following classes of invertebrate animals, viz., Spongida 

 (4 genera), Hydrozoa (2 genera), Actiriozoa (5 genera), Echinodermata 

 (i genus), Annelida (4 genera), Brachiopoda (10 genera), Lamelli- 

 branchiata (3 genera), Gasteropoda (-6 genera), Pteropoda (4 genera), 

 Crustacea (5 genera), Trilobita (15 genera). 



Mr. Walcott's list contains a larger number of classes and of 

 genera and species than is at present known in the Lower Cambrian 

 fauna on this side of the Atlantic ; but, with the exception of the 

 Lamellibranchiata, all the classes are now known to occur in the 

 Middle Cambrian either of Wales or Scandinavia. It will be seen 

 that Trilobita and Brachiopoda are the dominant classes, and this is 

 equally marked in the succeeding or Middle Cambrian fauna. The 

 Trilobita, especially, give to these faunas their very distinctive 

 characters, and the faunas are frequently referred to as the Olenellus, 

 Paradoxides, and Oleiius Zones after closely-allied genera, which also 

 are the most typical occurring in them. The genus Olenellus occurs 

 only in the Lower Cambrian, Paradoxides in the Middle Cambrian, 

 and Olenus in the Upper Cambrian. The order in v/hich they appear 

 in the succession is the same wherever they have been discovered in 

 all the American and European sections. 



^ Tenth Ann. Rep. U.S. Geol. Siirvey, part i., pp. 509-763, pis. 49-98 : 1890. 

 5 Bidl. U.S. Geol. Survey, no. 81 : 1891. 

 " Op. cit. nit., p. 372. 



