POSITIONS OF THE TETGONIiE OF J^OETH OXFORDSHIEE, ETC. 



47 



form I have referred to T. clatlirata, Ag., but differing in the curva- 

 ture and absence of undulation in the rows of costae. It varies 

 from Lycett's definition principally in the fewer rows of costse. 



EXPLANATION OF PLATE I. 



Fig. 1. Trigonia Lycetti. Inferior Oolite, Sharpshill, near Hook Norton. 



2. (example with solid costse). Same locality. 



3, yar. comigata. Same locality. 



^. j: yrthamptooicnsis. Upper Lias, Moulton, near Northampton. 



5, 6. — . Same locality. 



7. . ^ , — (specimen without transverse costge). Same locality. 



Discussion. 



Prof. JuDD expressed his sense of the great value of Mr. Walford's 

 work in showing the relations of the several divisions of the Infe- 

 rior Oolite of Oxfordshire as compared with the beds of the same 

 age in South Northamptonshire and in Gloucestershire. 



Dr. WooDWAED hoped that Mr. Walford's studies would enable us 

 to distinguish which of the forms described by Dr. Lycett should be 

 regarded as species and varieties respectively. He suggested that 

 the difficulties might to some extent be got over by employing a 

 trinomial nomenclature. 



Prof. Seelet pointed out the importance of defining the range in 

 time of fossil species with a view to fixing the geographical distri- 

 bution. The varieties of one district become representative species 

 in other countries. 



Mr, H. B. WooDWAED thought that some of the difficulties in cor- 

 relating subdivisions of the rocks would be removed if the strati- 

 graphical evidence were attended to as well as the palseontological. 



The AuTHOE agreed with Dr. Woodward in thinking that many 

 of the species of Dr. Lycett must be grouped as varieties. The 

 lithologicai evidence, to some extent, bears out the palasontolo- 

 gical evidence as to the relationship of the Fawler and Hook- 

 Norton strata. 



