6o SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 64 



Coosia are well represented in China, western North America, south- 

 western United States, and northwestern Europe. Bathyuriscus and 

 Asaphiscus are essentially Pacific Basin types. They represent the 

 most advanced forms of the Trilobita of Middle Cambrian time and 

 may be compared with Asaphus and Bathyurus of the Ordovician 

 fauna. 



Redlichia is an intermediate form that serves in a limited degree 

 to connect the Mesonacidse^ and the Paradoxidse. Its tapering 

 glabella and elongate eye-lobes recall those of Nevadia, and its small 

 pygidium that of Holmia and Callavia^ 



Many species of trilobites are represented only by fragments of 

 the cephalon, scattered segments of the thorax, and pygidia that 

 can only be tentatively designated as probably belonging to the same 

 species as an associated cephalon. In some instances the cephala of 

 otherwise distinct genera are so nearly similar that in the absence 

 of the thorax and pygidium they would be referred to one genus. 

 This is particularly the case among the genera of the Ptychoparidae. 



THE LARGER FAUNAL HORIZONS 

 The geographic distribution and characters of the Lower, Middle, 

 and Upper Cambrian divisions of the eastern and southern Asiatic 

 Cambrian faunas vary to such an extent as to make it desirable to 

 consider them separately. It seems from our present information 

 that the Cambrian sea first transgressed the southern and southeast- 

 ern sections of the continent in late Lower Cambrian time and that 

 certain changes occurred in its distribution at intervals during the 

 remainder of Cambrian time. The data, however, are still too lim- 

 ited to give more than very approximate limits to the distribution of 

 the faunas. Extended areal mapping of the distribution of the geo- 

 logic formations and faunas will be necessary before paleogeographic 

 maps of eastern Asia can be made that are more than broad outlines 

 to be changed and filled in very much as the geographic map of 

 Africa was modified from time to time during the last half of the 

 nineteenth century. 



Lower Cambrian fauna. — The Lower Cambrian (Man-t'o shale) 

 Redlichia fauna of Shan-tung, Shan-si, Yun-nan, and northern India 

 is, so far as known, very distinctive and confined to the Asiatic con- 

 tinent and Australia. 



^ Walcott, C. D. Smithsonian Misc. Coll., Vol. 53, Cambrian Geology and 

 Paleontology, No. 6, 1910, pp. 231-422, pis. 23-44: Olenellus and other genera 

 of the Mesonacidae. 



^ Idem, pi. 44. 



