170 E. G. Carrut/iers — A Revision of some Carhoniferons Corah. 



The occurrence is, however, strictly local, and I am not yet aware 

 of such corals in other parts of Scotland, though McCoj', as previously 

 noted, records an ajjparently similar form from " Carboniferous shale 

 near Glasgow." 



Distribution. 



Little can yet be said concerning the distribution of the species in 

 Britain. The only undoubted examples that have so far come under 

 my notice, have been found by Dr. Vaughan in the South- Western 

 Province. He writes : — 



" This species is confined in the South- Western Province to the top 

 of Z and C, that is, it immediately precedes and accompanies the intro- 

 duction of Caninia cylindrica ; its maximum lies immediately below 

 the first occurrence of the latter species. In the Gower the species 

 was noted in the Upper Z and 7 of the cliff section between Phossili 

 and the Worm." 



One or two fragments, possibly belonging to this species, have been 

 found by Dr. Matley in the Eush Slates of co. Dublin (locality R 6^), 

 but the}' are not sjjecifically determinable. 



Although the chief object of this paper has been a revision of the 

 species concerned, some aspects of the question of the zonal value 

 of such fossils, may be briefly noticed in conclusion. 



The usual habitat of these corals seems to have been a calcareous mud. 

 They commonly swarm in limey shales, but are comparatively rare in, 

 if not absent from, massive limestones. But no rule to this effect can 

 be given, and in Scotland, certainly, small rugose corals of this type 

 are noticeably local iu their distribution. In a bed whose position 

 is accurately known over a wide area, they appear and disappear in 

 a remarkable manner, as if they were very sensitive to conditions of 

 deposit and food supply. 



That they may be of the highest stratigraphical value over an area 

 where such conditions seem to have been constant, is not for a moment 

 to be disputed ; Dr. Yaughan's admirable work in the South-Western 

 Province supplies an excellent instance. But, as a rule, in correlating 

 over areas exhibiting lithological variation, the relative abundance or 

 scarcity of such corals is of no great value. More trustworthy' results 

 should be attained if some of these forms can be clearly proved to 

 have undergone some definite evolutionary change with the passage 

 of time, but until this can be done it would be safer to regard them 

 as untrustworthy for zonal purposes. 



The particular corals dealt with in the foregoing articles are of 

 a somewhat simple type, and their structure can hardly be expected to 

 admit of considerable modiBcation. Nevertheless, there is some evidence 

 that an evolutionary change did take place, and that it is, in a general 

 way, helpful to the stratigrapher. It is also alwa3^s possible that 

 aberrant types maj' be found of narrow vertical range, though in view 

 of the local occurrence of these corals, evidence apparently pointing to 

 such a fact should be received with caution. 



j!^ow that zonal work in the Lower Carboniferous rocks is being 

 actively prosecuted in many areas in Britain, it may be expected that 



