6 CARBONIFEROUS LAMELLIBRANCHIATA. 



example, in shale beds Prodvdus semireticulatus does not attain to the size which 



is characteristic of this species in the Mountain Limestone. Many similar 



examples can be quoted amongst the group of Lamellibranchs. I have pointed 



out in a previous Monograph^ how the size of Naiarlites crassa varies as it 



occurs in limestones or shales, and the same thing may be noted in the case of 



8chizodv,s SaJferi in the limestone at Randerston, Eifeness, and the shale at 



Woodhall, near Edinburgh. It is very interesting to note the dwarfed condition 



of those typically marine fossils which are contained in certain narrow bands in 



the Coal Measures of Lancashire and Staffordshire. These beds contain a fauna 



comparatively rich in species, most of which occur in the Lower Carboniferous 



rocks, demonstrating a prolonged survival in some external area until the marine 



conditions necessary for their existence recurred in these areas. The following 



list of fossils recognised as occurring' in the roof of the Gin Mine or Golden Twist 



of North Staffordshire has altogether a Lower Carboniferous facies : 



Discites suhsulcatus. Axinus {Scliizodiis), sp. 



Qoniatites excavafus. Ortlioceras, sp. 



— striatuR. Solemya jJrimaiva. 



— multilobus. Ghonetes Laguessiana. 

 Cypricardia glabrata. Nucula gibhosa. 

 Aviculopecten, sp. — lineata. 

 JEuomphalus tuberculatum. Leda clavata. 

 Pleurofomaria, sp. Macroclieilus BlicJiotianus. 

 Productus semireticulatus. Loxonema, sp. 



Spirifer TJrei. Belleroplion Duinontii. 



But most of the species are very much dwarfed, the Productus being very small 

 indeed. 



The marine fauna of the Pennystone beds of Coalbrookdale is very interest- 

 ing, both in point of view of its richness in Lamellibranch forms, and the fine 

 size to which these attained. The richest bed occurs about the middle of the 

 productive Coal Measures, and has altogether a Lower, Carboniferous facies, con- 

 taining Spirifer bistriatus, Produchis scabricuhis, Bhynchonella ijleurodon, Discina 

 nitida, Gonularia quadrisulcata, Peden, two species, Nucula, Nuculana (Leda), and 

 several species of Schizodus and other bivalves hitherto known as Sanguinolites, with 

 several species of Cephalopods and Gasteropods, some of which are of large size. 



This fauna, though not exactly identical, has a close resemblance to that of tbe 

 Redesdale Ironstone, which is generally considered to be about the horizon of the 

 Yoredale beds of Yorkshire ; the specific differences are not really greater than 

 might be expected to have obtained in forms surviving through long periods of 

 time, several species being common to the two deposits. 



^ Pal. Soc. volumes for 1894 and 1895, ' Monograph of Carbonicola, Anthracomya, and Naiadites,' 

 ])p. 9 and 150, 



