PRODUCTIDtE. 335 



Obs. This small species was in 1839 so briefly described by Mr. J. de C. Sowerby, 

 from an incomplete ventral valve, that I did not recognise by it the perfect examples 

 obtained in 1847 by Mr. Gray near Dudley. I was therefore unfortunately induced to 

 redescribe (with full illustrations) the species under the designation of Leptmna Grayii ; 

 and indeed I am not yet perfectly convinced that the last is not a well-marked variety of 

 Ch. minima,m which the ribs are less numerous and the shell much smaller. For instance, 

 in the typical example of Ch. minima (Ludlow) there are from twenty-five to twenty-six 

 })rincipal ribs, whilst in the var. Grayii (Wenlock) there are, upon an average, not more 

 than from twelve to sixteen. Ch. minima, is also a larger shell, and is much more 

 concavo-convex. 



Position and Locality. This small shell is stated to occur in the Upper Llandovery 

 (at Llangadock) and in the Wenlock and Ludlow formations. 



In the Wenlock Shales it is not very rare at Burrington, near Dudley ; at Bryn-mawr, 

 Mynydd Tryfan ; Capel-y-rhiw, &c. 



In the Woodwardian Museum, Cambridge, are specimens from Llanfair, Welshpool, 

 and Tynewydd Myddfoi ; also from calcareous flags, bed of the Dee, Llansilio, south of 

 Llangollen. 



In the Lower Ludlow at Elton Lane and Vinnal Hill, Ludlow, &c. 



I do not know of any foreign locality. The shell so named, from Bohemia, by M. 

 Barrande, does not belong to Sowerby's species. 



