244 



PROC. COTTESWOLD CLUB vol. xiii. (4) 



It almost seems necessary when speaking of this very 

 complete developmental series of the Jiiubria stock to have 

 certain names for the stages attained. They might be 

 subfimbria, fimbria, and perfimbria. 



Their characters might be defined as follows : — 



Terebr. S7ibfimbria. Truncate beak ; circular form of 

 shell, with slight fimbriation. Pea grit. 



Terebr. fimbria. Curved beak ; circular form of shell, 

 pronounced fimbriation. Oolite Marl. 



Terebr. perfimbria. Curved beak ; elongate form of 

 shell, excessive fimbriation extending over most of the 

 test. Upper Freestone. 



It need not be insisted upon that the advance towards 

 greater fimbriation is always uniform. It is not ; and it 

 would not be expected. But such advance is the general 

 tendency — the less fimbriate become scarcer and scarcer, 

 the more fimbriate become more numerous. 



How far the development of the fimbria series corre- 

 sponds with that of other fimbriate fossils may be seen 

 in the following Table : — 



Upper 

 Freestone 



" Ps. galeiformis, 

 var., "somewhat 

 fimbriate. 



T. perfimbria, 

 very fimbriate ; 

 elongate. 



Oolite Marl T. polypleda, T. fimbria, 



distinctly fimbri- distinctly fimbri- 

 ate ; elongate. ate ; circular. 



Pea Grit Ps. simplex, T. plicata, T. subfimbria, 



very slightly fim- slightly fimbriate ; slightly fimbriate ; 



briate, and that elongate. circular, 

 rarely. 



It is between T. polyplecta and T. perfimbria that 

 homoeomorphy is most marked ; but they are not truly 

 isochronous, they are slightly heterochronous. 



