140 MR. C. A. MATLEY ON THE CAMBRIAN [ Feb. 1902, . 
Dimensions.—Three specimens measured :— 
Length. Width. 
9 mm. 11 mm. 
7 83 
54 ies 
Horizon.—The specimens have been most abundantly obtained 
from the Black Shales and (?) from a band of foraminiferal lime- 
stone (M 218) included in them, but they occur also in the overlying 
Grey Shales. I have seen no examples from any horizon lower 
than the Black Shales. 
Observations.—Undoubted members of the genus Obolella, to 
which genus it is very doubtful that Holl’s species can be assigned, 
are not known to occur above the Lower Cambrian; but, until the 
generic position of this form can be fully established, its nomencla- 
ture may as well be left undisturbed. As will be seen from the 
figures, the specimens vary much in the proportion of length to 
breadth, but there are sufficient intermediate forms between the 
broad and narrow varieties to warrant the belief that we are dealing 
with a single species. All the specimens from the foraminiferal 
limestcne-band are exclusively of the broad type and are of large 
size, but the broad form is also found with those of less width in 
both the Black and the Grey Shales. 
Davidson saw only one example of this shell, which reminded 
him very strongly of Obolella? (or Obolus?) plumbea, Salter, and he 
seemed uncertain whether the two forms were distinct. The last- 
mentioned shell may, however, be readily distinguished by its 
numerous radial striz, which are absent from the exterior of 
O, Salteri. 
Holl’s figure (also reproduced by Davidson) shows a median line 
extending from the umbo for about two-fifths the length of the 
valve, suggesting a median septum or the impression of a pedicle-slit. 
The examples which I have been able to examine show that this is 
an udventitious feature, the result of the splitting of the shell under 
compression. Nearly all the shells from the shales show a splitting 
of the valves at the umbo, and in almost every case the crack is 
more or less oblique to the middle line, and sometimes extends to 
the front of the shell. 
According to Linnarsson,? Obolella Saltert forms in Sweden a 
zone above the Dictyonema-beds, and Prof. Brogger records the 
same species from the Ceratopyge-shales, Ceratopyge-limestone, and 
Phyllograptus-shales; but it seems very doubtful whether the 
Scandinavian fossil is identical with Holl’s species,* and moreover 
the Malvern species appears to be found most plentifully below 
the Dictyonema-horizon. 
1 There is some doubt about the identity of these limestone-specimens, on 
account of their large size and greater convexity. While most of them are no 
bigger than large examples from the Shales, there is one (incomplete) example, 
to which Prof. Groom has drawn my attention, which must have measured 
30 mm. across. As regards difference of convexity, the valves found in the 
Shales have probably been somewhat flattened by compression. 
2 See Lapworth, * Life & Work of Linnarsson’ Geol. Mag. 1882, p. 75. 
* See the figures in Brogger’s ‘ Die Silur. Etag. 2 u. 3 im Kristianiagebiet ” 
882, p. 44, pl. x. 
