APPENDIX. 117 



elevated line from the back to the basal margin ; stria? about twelve, very regular, and 

 nearly equidistant (bent at an angle of 90° at the umbonal slope). Length, ^ths, breadth, 

 nearly ^ths of an inch." " The shell is accompanied on the specimen with some obscure 

 impressed linear marks of a plant." 



The figures are reproduced here (PI. V, figs. 11, 12). The sandstone is referred 

 to the formation called No. XI by Prof. H. D. Rogers in the State Geological Survey of 

 Pennsylvania, and referred by him to the base of the Carboniferous system, but regarded 

 by some geologists as the uppermost part of the Devonian or Old Red Sandstone. In this 

 formation of sandstone (which, with its associated shales, is 3000 feet thick), Foot- 

 tracks of Reptiles, Rain-prints, Wave-marks, and Trails of Annelids or Molluscs are not un- 

 common' at two or more horizons. 



Leaia Leidyi, var. Williamsoniana. PI. I, figs. 19, 20. 



Bivalvulae Shell?, W. C. Williamson. Philos. Mag., new series, 183G, ix, p. 351. 

 Aptychus?, J. Phillips. Silur. Syst., 1839, p. S9. 



Inch. Inch. 



Height of valve . . . -^^A 



Length i Proportion 1 to 2. 



Length i j 



Height fi 



„ r Proportion 5 to 9, or 1 : 2 — 

 Length v %) 



This is very like Leaia Leidyi ; but, as it is much smaller, and appears to be still 

 neater in form, and to have a few more striae, and as it comes from the much higher 

 horizon of the Uppermost Coal-measures, and in England, I propose to treat of it separately, 

 as a variety under the above name, which will associate it with its well-known discoverer, 

 Prof. Dr. W. C. Williamson, F.R.S., of Manchester. 



The specimens lie dispersed in a soft grey shale, in considerable numbers, and are 

 not disposed on the planes of bedding. They are from the Uppermost Coal-measures of 

 Lancashire (Ardwick, near Manchester), and were confided to me for examination, in 

 1856, by Prof. Williamson, who believed them to belong to some nondescript Ento- 

 mostracan, if they should not prove to be Trigonellites. He found them many years age 

 and referred to them in a paper (on the Limestones found in the vicinity of Manchester) 

 published in 1836 iu the 'Philos. Magaz.,' new ser., vol. ix., from which the following- 

 extract has been taken. 



" In the blue clay immediately above the ' black bass ' are a series of remains, in 

 attempting to decide upon the nature of which I find myself completely puzzled. They 

 are very thin bodies of a brown colour, nearly square in their form, two of the corners 



1 See 'Boston Soc. Nat. Hist. Proceed.,' vol. v. p. 182, and Lyell's 'Manual of Geology,' 5th edit., 

 p. 379, &c. 



