216 
Yu Wen 
crossed by the radiating threads to form a 
cancellated sculpture. With the increase in shell 
size, the growth lines become progressively thicker, 
and the radiating threads more and more obscure 
on the margin of the valve. 
Shown in Figure 4 E-I is a nearly completely 
preserved internal mould. In plan view the valve 
appears subcircular and the apex is slightly broken. 
The traces of radiating costae can be seen on the 
margin of the valve. In the centre of the valve there 
is a longitudinal shallow depression, starting from 
the apex and gradually disappearing to the 
posterior. On the sides of the longitudinal shallow 
depression there are about four pairs of 
asymmetrically arranged ridge-like impressions 
and three concentric impressions (Figure 3). The 
direction of the ridge-like impressions is the 
reverse of the surface radiating costae. The first 
pair of ridge-like impressions are short and very 
obscure, situated near the apex. The second pair 
are situated at about two-fifths of the valve length 
from the adapical margin and gradually extended 
forward and inclined to the adapical margin; the 
left ridge-like impression is longer, and narrower 
than the right one. The third pair are similar 
morphologically to the second pairs, situated at the 
mid-length of the valve but longer and larger. The 
fourth pair is fainter and more obscure than the 
others, which is situated at about two-thirds of the 
valve from the adapical margin. The outer 
concentric impression is thin, forming a ring on the 
periphery. The middle one is stronger and shorter 
than the others; while the inner one is faint, 
gradually extending to the adapical side. 
Dimensions (in mm) 
LENGTH WIDTH 
NIGP 116388 7.00 7.50 
NIGP 116389 6.80 4.40 
Remarks 
In the general shape of the valve, this form 
appears to be similar to the type species Bagenovia 
sajanica Homy (Radugin 1937: 301, figs 5, 5a; Horn)' 
1957: 428, pi. Ill, figs. 1-6) from the Early Cambrian 
of west-Sayan, Siberia, but differs in the presence 
of more numerous radiating costae and in the 
subcircular outline. In apical view, this species is 
also similar to Bagenovia kazakhstanica Koneva 
(Koneva 1976: 127, Figure 1; 1979: 22, pi. II, figs. 1- 
10, pi. Ill, figs. 1-2) from the Early Cambrian 
Lenian Stage of central Kazakhstan. It can be 
distinguished by the coarser and more numerous 
radiating costae, and the undulating growth lines. 
The most important distinguishing feature of 
Bagenovia cf. sajanica is that the internal structure of 
the valve is characterized by four pairs of 
asymmetrically arranged ridge-like impressions 
and three concentric impressions on the dorsal 
valve of the cast. The internal structure of 
Bagenovia kazakhstanica possesses a longitudinal 
carina and more ridge-like short impressions and 
the presence of some small pits, especially near the 
apex. 
Occurrence 
Basal part of the Early Cambrian Xidashan 
Formation of Mohurshan, Kuruktag, Xinjiang and 
the Early Cambrian Shipai Formation of Suizhou, 
Hubei, China. 
ACKNOWLEDGEMENTS 
I wish to thank Zhang Sen-gui of the Nanjing 
Institute of Geology and Palaeontology, Academia 
Sinica for sending me the Xinjiang specimens, and 
K.J. McNamara, E.L. Yochelson and S. Conway 
Morris for reviewing the manuscript and making 
valuable suggestions. Thanks also to Song Zhi-yao 
and Mao Yong-qiang for preparing the 
photographs and to Ren Yu-gao and D. Hendricks 
for drawing the text-figures. 
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