THE LARGER FAUNAL HORIZONS. 49 



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 southeastern sections of the continent in 

 late Lower Cambrian time and that certain changes occurred in its distribu- 

 tion at intervals during the remainder of Cambrian time. The data, however, 

 are still too limited to give more than very approximate limits to the distri- 

 bution of the faunas. Extended areal mapping of the distribution of the 

 geologic formations and faunas will be necessary before paleographic 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 continent and Australia. 



The fauna is unknown in Manchuria, although Blackwelder considered 

 that the Yung-ning sandstone of southern Liau-tung was probably of Lower 

 Cambrian age. [Blackwelder, 1907, p. 87.] 



In this and the following lists I have combined the local lists, placing 

 after each species the locality number, so that each species may be traced back 

 to its local list and thus found with its immediate associates in the strata. 



In Central Shan-tung the Man-t'o sandstones contain a small fauna, as 

 follows : 



Billingsella richthofcni (Cj,, 20) Redlichia sp. undt. (C6) 



Obolella asiatica (Ciy, 32') Ptychoparia aclis (Ciy, 20, 31) 



Hclcionella rugosa chinensis (C$) Ptychoparia, granosa (C 17) 



Hyolithes delia (3) Ptychoparia impar (C 17) 



Hyolithes sp. undt. (032') Ptychoparia ligea (31) 



Redlichia chinensis (C 15, C 16, 027) Ptychoparia (Emmrichella) constrida (3) 



Redlichia nobilis (3) Ptychoparia (Emmrichella} mantoensis (C2O, 31) 



Of the above, Obolella asiatica, Helcionella rugosa chinensis, and Redlichia 

 chinensis may be considered as characteristically Lower Cambrian. I do 

 not know of the occurrence of the genus Obolella above the Lower Cambrian 

 [Walcott, 1912, p. 588], and Helcionella rugosa belongs to the same fauna. 

 Redlichia chinensis and R. nobilis have been referred to as descendent from 

 Olenellns [Walcott, 19100, p. 254], but I would now cite Callavia in place of 

 Olenellns, as the latter genus appears to have left no descendants. It should 

 also be noted that the very ancient form Nevadia has a tapering glabella and 

 long eye-lobes [Walcott, 19100, plate 23], which leads me to consider Redlichia 

 as an example of reversion to a more primitive type in the form of the glabella. 

 The thorax and pygidium of Redlichia are more like the same parts in Wanneria 

 [Walcott, 19100, plate 30], except for the median spines of the thoracic 

 segments. 



