EDMONDTA PUNCTATELLA. 1 17 



much smaller size than Anthracomya Phillipsii. The species which it most nearly 

 resembles is A. minima, Ludwig, which is flatter, more triangular, and has a much 

 shorter hinge-line. 



I am of opinion that A. calcifera is of distinct value as indicating a special zone, 

 and it appears to be the only molluscan form present in that zone. It has not yet 

 been discovered in beds which contain A. Phillvpsii. A. calcifera is present in very 

 large numbers at certain horizons in its zone of occurrence, but it is very sparsely 

 distributed through the rest of the rock of its zone. 



The zone of A. Phillipsii is much more extensive, and altogether below that of 

 A. calcifera. The zone of A. calcifera occurs 300 feet below the Penkhull Sand- 

 stone, estimated to be about 900 feet above the Bassey Mine Ironstone, which itself 

 is filled with crushed specimens of A. Phillipsii. The Penkhull Sandstone is 

 underlain by a series of grey sandstones and grey marls with the zone of A. 

 calcifera at their base : these were included by the officers of the Geological Survey 

 in the Upper Coal Measures. They are underlain by a series of clays and marls, 

 worked for brick- and tile-manufacture. 



It is very difficult to separate A. calcifera from the hard matrix of the lime- 

 stone, and unless this be done its characters are often hidden. With its posterior 

 angle hidden, the shell may be easily mistaken for a species of some other genus, 

 especially Carbonicola. In specimens from the limestones, also, little evidence is 

 shown of the wrinkled periostracum, so characteristic of the genus, but when 

 preserved in a more shaly matrix undoubted evidence of this condition obtains. 

 Occasionally, too, the shells are crushed and flattened, and then assume a shape 

 very different from that which really belongs to them, becoming much more 

 triangular ; while the posterior end, on account of its natural convexity, appears 

 much expanded from above downward. 



Edmondia punctatella, Jones, sp., 1865. Plate XXV, figs. 12, 13. 



Estheria punctatella, Jones, 1865. Trans. Geol. Soc. Glasg., vol. ii, pt. 1, 



p. 71, pi. i, figs. 5, 5 a. 



Posidonomya punctatella, Jones, 1891. Trans. Geol. Soc. Glasg., vol. ix, pt. i, 



p. 83, pi. v, figs. 7 a, 7 b. 



Specific Characters. — Shell of medium size, transversely sub-ovate, inequi- 

 lateral. The anterior border is irregularly rounded, passing with a continuous 

 curvature into the inferior margin, which is gently convex. The posterior margin 

 is truncately rounded, sometimes almost straight above, where it meets the hinge- 

 line at a more or less marked obtuse angle. The upper margin is shorter than the 



