Palceozow Fossfls. 369 



of either S'p.'orhi(/nyi or S'j). antardicys. Mr. A. G. Bain when 

 he read his i)aper to the Geological Society in 1852, only sub- 

 mitted a selection of his fossils which were described by Messrs. 

 Sharpe and Salter. From an examination of the remainder in the 

 Albany Museum, and of the fossils collected by Dr. Atherstone, 

 I have come to the conclusion that apart from the vagaries of 

 apparent structure produced by distortion, the shells of the Spii'ifers 

 wei-e very susceptible to the nature of the sea bottom on which 

 they grew. The natui-al floor was that on which the calcareous 

 sandstone was deposited, which now forms the fossiliferous sand- 

 stone ; in an area in which mud was being laid down, the shells 

 grew to a far larger size, but were thin and irregular, and the 

 specimens I obtained fi-om the Slangfontein I'oad quarry, which 

 have been called Spirifcr ccresi by Reed, are examples of shells in 

 this condition. Between the two extremes we find every gradation, 

 and the thicker the shells the wider the hinge area, and the thinner 

 they are the narrower this becomes ; I cannot, therefore, see any 

 specific significance in the depth of the hinge area, which, more- 

 over, is very seldom seen, as the specimens are usually internal 

 casts. In the exact number of ribs, angulation of the sinus, 

 tnedian fold and rilis, also, I see no specific characters : for 

 instance, in the two figures of Mr. Reed's Spiriffr ccrrs, one has 

 rounded, the other distinctly angular rilis, wliereas in his Spii'ifi'r 

 jx'dnxinufi his oidy difl'erence between this form and the Spiriff/- 

 antairticKx of Morris and Sharjjc, besides the width of the hinge 

 area, is the more rounded form of the ribs. The whole difficulty 

 of this troublesome business is the unsatisfactory nature of the 

 fossils, and the fact that both Shar[)e and Reed had only selections 

 from larger collections to u oi-k from. I have a strong suspicion 

 that had we a larger number of actual shells instead of merely 

 casts, a half a dozen varieties could l)e separated out. Taken as a 

 whole, the Bokkeveld Spirifers hav(^ atlinities with North and South 

 American foi-ms. The Australian species refeired by Ktheridge' to 

 the forms Sp. bisu/cata, Sow, and Sjk inidi/eid rar. inidn/at((, V. 

 Roemer, have some resembhmces respectively to *S/^. (ni/a/vficus 



iQ.J.G.S., Vol. XXYIII., p. ■A'29-:y.H), PI XVI., figs. 1, So. 



