40 PROCEEDINGS OF THE 



eminent palaeontologist, states that the variety, ;S'. Vmilcata, has 

 been by some assimilated with the Devonian S. aperturata, to 

 which it approaches somewhat closely in form. I think that not 

 only this species, but many others, may have been derived from 

 Devonian forms by descent. Thus, amongst others, our abundant 

 Spirifera Urii is believed to be identical with the Devonian 

 S. unguiculus, and it has also been shown that it survived along 

 with some other Carboniferous species until Permian times, in 

 which formation it is known as Sjnrifera Clannyanus. In the lower 

 limestone shales of the Beith district, Spirifera trigonalis on its first 

 appearance presents us, as will be seen by the specimens exhibited, 

 with at least three or four well-marked varieties, one of which 

 has the mesial fold more produced than any yet described. This 

 variety I have found in the upper cement limestone at Arden, 

 near Thornliebank. One of the other varieties approaches closely 

 to Sjnrifera acuta, which has not yet been identified from Scotland; 

 the others agree with the typical varieties, S. trigonalis and 

 S. hisulcata, although some of the latter are more transverse than 

 are usually found. In the shales at Newfield, High Blantyre, a 

 variety of S. trigonalis is found, which, in the extension of its 

 hinge-area and elongated mesial fold, almost rivals that of S. 

 triangtilaris, from which species it is known by its more numerous 

 ribs. This wide variety is there the only form of the species that 

 has yet been found. I also exhibit specimens of the ordinary 

 varieties of >S'. trlgo7ialis and S. Usulcata, frou;i both the lower and 

 upper limestone series of the west of Scotland; the species, as I 

 formerly stated, ranging upwards into the millstone grit, being- 

 found in the sandstone and shales of that group to the north-east 

 of Glasgow. 



One of the largest and finest varieties of Sjnrifera hisulcata 

 obtained in the west of Scotland, is that found in the shales 

 overlying the cement limestone at Orchard, near GifFnock, on the 

 Busby railway. The strata belong to the upper limestone series, 

 and this form, so far as yet known, seems to be peculiar to that 

 horizon. It is very deep between the valves, and comes very near 

 to Spirifera onosqiiensis, a species not hitherto recognised from 

 Scotland, being only distinguislied from it by its fewer ribs. It 

 is very probable that all these varieties of Spirifera trigonalis are 

 only varieties produced by descent from one original type, which 

 seems to have been very variable, the variations probably being 



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