54 RESEARCH IN CHINA. 
The Middle Cambrian fauna, like that of western North America, is much 
larger and more abundant than that of the Upper Cambrian. This was 
due in a considerable degree to the usually favorable conditions existing on 
account of the great variety of habitat afforded by the seas of the period. 
The advancing and deepening Middle Cambrian sea forced the local faunas 
to change their habitat from time to time and they had either to adjust them- 
selves to the new conditions and habitat or to perish. Local isolation for long 
periods led to the development of new forms, and these, when the barriers were 
removed, contested and competed for their position and existence with other 
faunas until, by a process of elimination of those least fit to survive, the 
development was hastened of a large and varied fauna. By the close of the 
Middle Cambrian more stable conditions prevailed and the era of rapid evolu- 
tion was checked until, under the impulse of new conditions of environment 
and accumulated tendency to change following the close of the Cambrian, 
a great evolution of new forms of life began. 
Upper Cambrian Fauna.—The geographic distribution of the formations 
containing this fauna is the same as for the Middle Cambrian, so far as now 
known. In the Sin-t’ai district the upper shale (Ku-shan?) and its fauna 
serve to form an upper horizon to the Middle Cambrian. The first fauna 
above the Ku-shan shale occurs in a limestone and, although only ro feet 
(3 m.) higher in the section, is entirely distinct from that of the Ku-shan 
shale. In includes the following: 
Billingsella pumpellyi (C61) Chuangia fragmenta (C61) 
Proampyx burea (C61) Chuangia nitida (C11) 
Pterocephalus busiris (C61) Ptychaspis baubo (C61) 
Chuangia batia (C11, C33a, C61) Anomocarella bergioni (C 33a) 
Sixty feet (18 m.) above the Ku-shan shale the fauna includes: 
Chuangia batia (C11, C33a)  Chuangia nitida (C11)  Anomocarella bergioni (C 33a) 
In the Ch’ang-hia district, at about 100 to 120 feet (30 to 36 m.) above 
the base of the formation, the fauna is relatively large and varied. It includes 
the following: 
Obolus matinalis ? (C54) Pterocephalus busiris (C54) 
Obolus (Westonia) sp. undt. (C56) Pagodia bia (C56) 
Discinopsis sulcatus (C 56) Pagodia dolon (C41) 
Eoorthis pagoda (C54, C56) Pagodia lotos (C56) 
Syntrophia orthia (C54, C56) Pagodia macedo (C34) 
Scenella sp. undt. (C56) Menocephalus ? depressus (C49, C56) 
Matherella circe (C56) Ptychas pis brizo (C38) 
Pelagiella pagoda (C56) Ptychas pis cadmus (C 41) 
Orthotheca sp. undt. (C56) Ptychas pis calchas (C 41) 
Cyrtoceras cambria (C56) Ptychas pis calyce (C 42) 
Agnostus sp. undt. (C34) Ptychaspis campe (C 42) 
Conokephalina belus (C56) Ptychaspis ceto (C34, C38, C54, C56) 
Conokephalina dryope (C56) Ptychaspis sp. undt. (C54) 
Lisania sp. undt. (C41) Coosia carme (C 38) 
