214 
Yu Wen 
Surface of the shell ornamented by prominent, 
irregularly spaced coarser or finer growth lines. 
Remarks 
Although Stenothecoides sp. from the Early 
Cambrian Xidashan Formation in Kuruktag is an 
incomplete specimen, it represents a bivalved 
stenothecoid with distinct characteristics: the 
narrowly elongated and asymmetrical dorsal valve; 
the apex curves anticlockwise during growth and 
with irregularly spaces growth lines. This species 
should be unquestionably assigned to the genus 
Stenothecoides. 
This form is very similar to Stenothecoides sp. 
from the upper Lower Cambrian of Siberia 
(Yochelson 1969: 51, figure 1) in such characters as 
the narrowly elongated dorsal valve, the pointed 
apex and the convex dorsal valve, but differs from 
the latter in the proportion between the length and 
width of the valve, in the more rounded posterior 
and in the coarser growth lines. In plan view, this 
species somewhat resembles Stenothecoides carinalus 
Koneva (1979: 27-28, pi. VI, figs. 5, 6) from the 
Early Cambrian Lenian Stage of central 
Kazakhstan, differing in the slender and more 
curved valve, in the narrower abapical margin and 
in the irregularly spaced growth lines. It is also 
allied to Stenothecoides elongata (Walcott) (1886: 129, 
pi. 12, figs. 4 a-b (not figure 4); Resser 1938: 24; 
Rasetti 1954: 63, pi. 11, figs. 3, 4), but differs from 
the latter in the more bent dorsal valve, in the 
wider abapical margin and in the irregularly 
spaced growth lines. 
Occurrence 
Basal part of the Early Cambrian Xidashan 
Formation of Mohurshan, Kuruktag Mountains, 
Xinjiang, China. 
Genus Bagenovia Hom^, 1957 
Bagenovia cf. sajanica Hom^, 1957 
(Figures 3, 4 A-I) 
Bagenovia sajanica Radugin, 1937: 301, fig. 5, 
(nomen nudum). 
Bagenovia sajanica var. raricostata Radugin, 1937: 
301, fig. 5a (nomen nudum). 
Bagenovia sajanica Homy, 1957: 428, pi. Ill, figs. 1-6; 
Knight and Yochelson, 1960:183, fig. 50, 8. 
Bagenovia multicostata Yu, in Zhang, 1983: 10 
(nomen nudum); Gao el al., 1984: pi. IX, figs. 6, 
9 (nomen nudum); Yu, 1986: 10 (nomen 
nudum). 
Material 
Three specimens, NIGP 116388-116390 in the 
Figure 3 Bagenovia cf. sajanica Horny, showing the 
internal structures, X 8. 
collections of the Nanjing Institute of Geology and 
Palaeontology, Academica Sinica. NIGP 116388 
and 116389 were collected in 1978 by Zhang Sen- 
gui from the base of the Early Cambrian Xidashan 
Formation on the northern slope of the Mohurshan 
of the Kuruktag Mountains, Xinjiang, China. NIGP 
116390 in the Nanjing Institute of Geology and 
Palaeontology, Academia Sinica, was collected by 
a geological party from the Geological Bureau of 
Hubei from the Early Cambrian Shipai Formation 
of Suizhou, Hubei, China. 
Diagnosis 
Subcircular, slightly asymmetrical, apex pointed, 
slightly curved anticlockwise during growth, with 
twenty-two pairs of radiating costae from the flat 
keel. There are four pairs of asymmetrically 
arranged ridge-like impressions and three 
concentric impressions visible on the dorsal valve 
of the internal mould. 
Description 
Valve of medium size, slightly asymmetrical. 
Moderately convex, subcircular in plan view. Apex 
small, pointed, distinctly protruding and 
overhanging the adapical margin; slightly curved 
anticlockwise during growth. In plan view, the 
individual valve tends to be narrowly rounded 
adapically, broad rounded abapical margin, with 
the greatest width of the valve at about one half of 
the length. A distinctly flat keel situated near the 
median part of the dorsal valve, which gradually 
flattens and widens to the abapical margin. From 
the flat keel about twenty-two pairs of costae 
radiate. They are small and short in the adapical 
part, with sharp crests, separated by wider 
depressions and curved forward, gradually 
becoming larger and longer in the middle part and 
gradually crowded, indistinct abapically, with 
obtusely rounded crests and separated by the 
narrower depressions. Radiating threads which can 
be observed in the flat keel very fine and dense 
(Fig. 4B). Growth lines very fine and undulating; 
