part 2] SYBINGOTHYRIS AND SPIlRIFElilNA. 227 



Fig. 13. Tylothyris Iwmmosa, inut. y. Interior of the pedicle -valve. Horizon y; 

 near Lavernoek (Glamorgan). (Coll. of Principal .T. F. Sibly, 

 20474 G8.) 



14. Spiriferina walcotWD'OTbigny. Internal cast of pedicle-valve. Lower 



Lias ; Radstock (Somerset). (Coll. of the writer, now in the Na- 

 tional Museum of Wales. Reg. No. 19246 G 9.) 



15. Tylothyris subconica siibconica. Interior of pedicle-valve. D., sub- 



zone ; Waterhouses (Staffordshire). (Coll. of Principal T. F. 



Sibly, 20474 G 9.) 

 1(5. Tylothyris laminma (M"Coy). Portion of the surface of a specimen 



retaining the imbricate structure, enlarged. Z zone ; Hook Head 



(Wexford). (Coll. of Geological Survey, London. Reg. No. 28425.) 

 17. Spirifer plicatosulcatus, sp. nov. (a) Brachial valve ; (b) the area. 



D, probably D., subzone ; Beeston, near Waterhouses (Staffordshire). 



(Coll. of Geological Survey. London. Reg. No. 28422.) 



Discussion. 



Dr. F. A. Bather congratulated the Author on the thorough- 

 ness of the methods used in his study. He had understood the 

 Author to say that the forms of Syringothyris merged one into 

 the other, and he enquired whether that statement referred to 

 contemporaneous varieties and species, or to successive mutations. 

 Was it possible to observe recapitulation of previous stages in the 

 ontogeny of the later forms ? 



Principal T. F. SlBl/r welcomed this important contribution to 

 Carboniferous palaeontology, and expressed his appreciation of the 

 value to zonal stratigraphy of the Author's careful and detailed 

 researches. 



The Author stated, in reply to Dr. Bather, that the variations 

 of Syringothyris in a vertical sense were gradual and continuous, 

 while at any one horizon forms belonging to either of the two 

 species enumerated could be easily distinguished, when they occurred 

 in normal deposits. Owing to the absence of suitable material, a 

 study of recapitulation had not been possible. 



In conclusion, the Author expressed his appreciation of the 

 encouraging remarks made by the speakers in the Discussion, and 

 thanked those who, by the loan of material, had made the work 

 possible. 



