366 DK. WHEBLTON HIND ON BRITISH [Aug. 1 899, 



this fold the valve is rapidly compressed and expanded to form the 

 dorsal slope. 



Interior. — Hinge edentulous. Muscle-scars normal. Pallial 

 line entire, remote from the margin. 



Exterior. — The shell appears to he almost smooth, but under 

 the microscope faint concentric lines of growth are to be observed. 

 Periostracum wrinkled. Ligament external, small, lodged in a 

 narrow groove^ 



Dimensions. — Antero- posteriorly, 6 mm. ; dorso - ventrally, 

 3 mm. ; elevation of valve, 1 mm. 



Localities. — A bed of freshwater limestone at Highfield marl- 

 pit, Etruria, and excavation for telegraph-posts, roadside, Bradwell ; 

 marl-pit east of Cocknage Hill ; railway-cutting, Florence Colliery ; 

 road-cutting, from Trentham to Whitmore, close to Butterton New 

 Earm ; Newcastle-under-Lyme railway-cutting ; Etruria, road- 

 cutting ; quarries near Longport Station ; marl-pit, Eichmond Hill, 

 Stoke-on-Trent; Upper Coal Measures, Slade Lane, Fallowfield, 

 Manchester coalfield. 



Observations. — This species is much more elongate, less 

 oblique, and attains a 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 moUuscan form present 

 in that zone. It has not yet been discovered in beds which contain 

 A. PhilUjpsii. 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 niuch more extensive, and altogether 

 below that of A. calcifera. The zone of A. calcifera occurs 300 feet 

 below the PenkhuU Sandstone, mapped by the officers of the 

 Geological Survey as Permian, and 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 under- 

 lain 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 limestone, 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; wLile the posterior end, on account of its natural 

 convexity, appears much expanded from above downward. 



