NORTH AMERICAN PALEONTOLOGY. 



279 



Walcott, Charles Doolittle — Continued. 



And also the table ou page 62, as follows : 



Zoologic resume. 



Algfe 



Spongiae 



llj'driizoa 



Crinoidea 



ATiiielida 



Brachiopoda 



Lauiellibianchiata 



Gasteropoda 



Ptoropoda 



Crustacea 



PcBcilopoda 



Genera. Species 



On page 63 a table of the classification of the North American Cambrian rocks 

 shows that the Cambrian includes the Potsdam sandstone and the Lower 

 Calciferous of the New York Survey as its npper member, and the Paradox- 

 ides beds of Braintree, Massachusetts, St. John, New Brunswick, and St. 

 John's, Newfoundland, as the basal member, and the Georgia formation as 

 the middle division. 



The geologic sections given in the introduction show the Cambrian system "to 

 have a total thickness of over l':^,000 feet, and that its middle division has 

 a known fauna of 43 genera, represented by 107 species ; also that the Lower 

 Cambrian or Paradoxides fauna has 32 genera and 76 species ; that the Upper 

 Cambrian or Potsdam fauna includes 52 genera and 2128pecies ; that of the 

 393 species now known from the Cambrian rocks but very few pass np into 

 the Calciferous horizon of the Lower SIUt-^ ^Ordoviciau), and that the 

 faunas of the two systems are so dis*^!r ., lU their general faciei, and also in 

 detail, that they are quite as readily separated as the Silurian and Devo- 

 nian, or the Devonian and the Carboniferous." 



Ninety species, eighteen of which are new, are described and illustrated, and 

 three new genera are proposed — Leptoviitns * (Spongite), Orijctocephalus,'! 

 and Protypus (Trilobita). The almost nnknown genera EihrnophnUnm, 

 Meek (Spongi;e), and Olenoides, Meek (Trilobita), are described ; and the 

 genus Microdisciis, Emmons (Trilobita) is redefined and based on another 

 species, as its type species is considered to be an embryonic form of Trtnu- 

 cleus concentric us. 



Paragraphs 119 and 120, page 57, state that : " Reviewing the Middle Cambrian 

 fauna as a whole, we find that it combines the characters of both the Lower 

 Cambrian and the Upper Cambrian faunas, and yet is distinct from either 

 of them. There does not appear to be an eqnivalent fauna in the Cambrian 

 system of Europe, either in Bohemia, the Scandinavian area, or in Wales. 

 The nearest approach to it is on the island of Sardinia." (See close of re- 

 marks on the genus Ethmophylliim, p. 80.) 



"The conditions that developed the Middle Cambrian fauna appear to have 

 been largely peculiar to the American continent. During the deposition 

 of the St. John seriesof the Lower Cambrian or Paradoxides strata, we learn 

 from the European and eastern American section that the fauna was essen- 

 • tially of the same type over the entire basin (Atlantic), and from the evi- 

 dence known to date that the fauna did not extend west of a line passing 

 northeast through eastern Massachusetts to New Brunswick and Newfound- 

 land." 



The illustrations are wood-cuts, and are very good of their kind. 



* Leptos (fine), mitos (thread). 

 t"0/3y%ro? (furrowed), and MEcpuX'ij (head). 



