20 a Portion of fibrous shell, tissue of ditto, magnified. 



20 b Entering valve of same specimen, shewing the smooth space near the beaks free of ridges, and the slight 



unusual appearance of a branch or supplementary rib at the margin. 



20 c Profile of same specimen. 



21 Highly typical specimen, shewing the great height of the sinus, &c. ; from the carboniferous limestone of 



Lowick, Norttnimbcrland. 



20* ATHYRIS GREG ARIA (M°Coy). Abnormal ovate variety, with small beak, front view; natural size, from 



the limestone of Kendal. 



20* a End view, shewing the very slight wave in the front margin. 



20*6 Profile. 



20* c Surface strongly magnified, shewing the fibrous tissue, and the longitudinal obtuse stria. 



22 SEMINULA FICUS (M-^Coy). Natural size, profile. 

 22 a View of entering valve. 



22 4 End view, shewing the undulation of the front margin. 



22 c Punctured surface, magnified. 



23 SEMINULA VIRGOIDES (M'^Coy) ; from the limestone of Isle of Man, end view, natural size (most specimens 



shew a greater upward curve in the front margin). 



23 a Same specimen, side view. 



23 h Receiving valve. 



23 c Shewing traces of the internal ridges of the entering valve, with a portion of shell near the front edge. 



23 (^ Surface, magnified to shew the reticular marking between the punctures. 



24 HEMITIIYRIS LONGA (M'Coy). Front view, natural size ; from the carboniferous limestone of Derbyshire. 

 24 « Profile. 



24 h Front view of entering valve. 



24 e Fibrous tissue of the surface, magnified. 



25 SPIRIFERA FASCICULATA (M"Coy). Natural size, from Derbyshire, profile. 



25 a Same specimen, entering valve (the cardinal area seeming slightly too wide). 



25 h Receiving valve. 



25 c End view, shewing the sinus in the front margin. 



26 SPIRIFERA PAUCICOSTATA (M"Coy). End view, natural size, from the limestone of Derbyshire. 

 26 « Profile. 



26 I Front view. 



27 SPIRIFERA ORNITHORHYNCIIA (M'Coy). Receiving valve of immature specimens, in which the mesial 



prolongation is not fully developed ; the cyhndrical sides both broken off; natural size, from the carboniferous 

 limestone of Derbyshire. 



27 « • Profile of both valves. 



28 SPIRIFERA OVALIS (var. hemispherka). Side view, natural size, from the Isle of Man, shewing the 



great inequality of the valves. 

 28 a Same specimen, shewing the entering valve and very small hinge-line and cardinal area. 



28 h Same specimen, front view. 



29 SPIRIFERA GRANDICOSTATA (M'Coy). Natural size, receiving valve (the four or five ridges on each side 



of the middle are not quite large enough to shew the abrupt change from them to the very small lateral 

 ones). From the carboniferous limestone of Derbyshire. 

 29 a Front view. 



29 I Entering valve, the four or five ridges, next the middle on each side, not quite large enough. 



30 LEPT I'.NA {Chonctes) POLITA (M°Coy). Magnified four diameters, shewing the very coarse scattered punc- 



tures, and small mesial septum of the internal cast, and the thick shell, and smooth external surface, on the 

 lower right-hand portion. The line above indicates the natural size. From the dark lower carboniferous lime- 

 stone of Lowick, Northumberland. 



31 LEPTiENA (C/tonetes) SUBJIINIMA (M'Coy). From the black limestone beds over the main carboniferous 



limestone of Derbyshire; magnified six diameters; the lower and right-hand portions shew the external shell, 

 and longitudinally sulcated surface, the remainder of the figure shews the close lines of strong punctures, and 

 small mesial sulcus of the beak, as exhibited on internal casts ; the line above shews the natural size. 



32 DISCINA BULLA (M'Coy). From a reddish bed of the impure lower carboniferous limestone of Lowick, North- 



umberland. Profile, natural size. 



32 a Same specimen, seen from above. 



33 LINGULA LATIOR (M'Coy). Natural size, from the black beds over the main carboniferous limestone of 



Derbvshirc. 



