found m the Vicinity of Manchester. 351 



this shell, I found a single specimen in the blue clay which 

 contained the Sphcnophyllum ; and in one of the thin seams of 

 red clay, above the first limestone, they are also to be met 

 with, though of a smaller size. Dr. C. Phillips found them 

 at Pendlebury, in the fragment of shale containing the Pla- 

 norbis. This was the circumstance that first induced the 

 above gentleman to differ from former observers in his opinion 

 as to the relative position of the Ardwick limestone, separating 

 it from the saliferous and connecting it with the carboniferous 

 group of rocks, an opinion of the correctness of which there 

 remains not the slightest doubt. 



My friend Mr. Joshua Alder, of Newcastle, informs me that 

 he has met with an Unio, closely resembling our specimens, in 

 the coal strata at the above place. This shell differs from the 

 U. nuciformis of Burdiehouse in being broader and wider in 

 proportion to its length, as well as in being a more fragile and 

 delicate shell. I am inclined to think it is an undescribed 

 species; if so, I would propose the name of Unio Phillipsii 

 as a slight return, not only for the private kindness I have met 

 with from Dr. C. Phillips, but for the service that gentleman 

 has done to geology by his indefatigable exertions in investi- 

 gating the nature of these limestones, as well as being under 

 his guidance in a district new to me when I first discovered 

 this most characteristic shell. 



Towards the upper portion of the third limestone is found 

 a thin seam of comminuted fragments of shells, amongst which 

 may occasionally be found traces of more perfect specimens. 

 These bear a close resemblance to, if they are not absolutely 

 the same as, the fossil now under consideration. From the se- 

 veral localities where these shells are found, and from their 

 extreme abundance, combined with the rarity of other Mol- 

 lusca of equal size, they must have formed an important feature 

 of the fresh waters of that early aera. 



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 being angular, and the opposite one rounded : I 

 have some nearly a quarter of an inch across. At first I 

 imagined that these were scales of fish, but now think they 

 must be same bivalvular shell. Their surface is marked with 

 strong concentric ridges, and passing from the hinge (?) to 

 the opposite corners, are two diverging elevated lines. I can- 

 not detect any traces of teeth, but liave found several specimens 

 in which the two valves (?) were connected at the hinge, and 

 the four ridges commencing from one common point in the 

 centre and diverging two each way : these I pointed out to 



