part 2] SYRINGOTHYRIS AND SPIllIFEIWSTA. 181 



interesting to record in this connexion that the examples of 

 Syringothyris from the Cracoe knolls much more closely resemble 

 those from the Irish Waulsortian knoll-phase limestones, than 

 those from the Derbyshire ' brachiopod-beds.' Nevertheless, the 

 special characters of the specimens from the Waulsortian knolls 

 and the ' brachiopod-beds ' are dependent upon the existence of 

 special conditions rather than upon the time at which these condi- 

 tions occur, and it is not safe to base conclusions as to the age of 

 the rocks upon forms of Syringothyris alone. 



Shells exactly resembling the Castleton type occur at Little 

 Island (Cork), in beds which, in age, probably correspond closely 

 with those at Castleton. In the list of fossils from the 

 Carboniferous Limestone from the vicinity of Cork given in 

 ' The Geology of the Country around Cork & Cork Harbour,' l 

 the fossils from all horizons are tabulated together ; but some of 

 them suggest the presence of beds of Dibunophyllum age, and 

 several of the fossils enumerated are characteristic of the Middle 

 and Upper Dibunophyllum Subzones in the Midlands. In common 

 with most of the fossils from the neighbourhood, the specimens 

 of S. cuspidafa are curiously distorted by pressure ; but their 

 similarity to the Castleton shells is verv apparent (see PI. XII, 

 figs. 2 a & 2 b). 



The genus has not yet been found anywhere in rocks later in age 

 than the Dibunophyllum Zone. 



Summary of Notes on the Distribution of 

 Syringothyris. 



From this account of the distribution of Syringothyris, it appears 

 that in the South- Western Province, where there was no marked 

 alteration in the conditions of deposition from Gleistopora to 

 Lower Oaninia times, the changes in the genus were continuous 

 and progressive. In common with many other brachiopod genera, 

 it disappeared from that area after the commencement of the 

 special conditions which prevailed immediately before and during 

 Seminula times, and never reappeared there. In other areas, 

 factors such as migration and the occurrence of abnormal conditions 

 of deposition render the sequence less clear. 



In Ireland, the genus becomes increasingly important from the 

 Gleistopora Zone, where it is very rare, to the Ganinia Zone, and 

 is seldom met with at higher horizons. In the Midlands and North 

 of England it is not present in the lowest beds of Carboniferous 

 Limestone, but appears in the Ganinia Zone in the North, and in 

 the Dibunophyllum Zone in the Midlands. Here, as in Ireland, 

 for reasons which have already been given, variations due to time 

 alone cannot definitely be distinguished. 



The genus illustrates in an interesting way some of the principles 

 of evolution. The (plrylogenetically) young stage with small and 



1 Mem. Geol. Surv. 1905, pp. 29-31. 



