238 PROC. COTTESWOLD CLUB vol. xiil. (4) 



Others where another character, valve-thickening* is, and 

 comes later. So again multiplication is an old age feature 

 in some Rhynchonellcr, it is a normal and very youthful 

 feature in most of them. 



Multiplication as an old age character pertains to the 

 fimbriate fossil figured by Mr Upton. The interesting 

 point about his discovery is this. There were already 

 known in the Inferior Oolite two nearly related fossils 

 showing homoiomorphy — namely, Terebrattda plicata and 

 T. fimbria. They both develop similar multiplication ; 

 yet it is obvious from their beak characters and general 

 shape that they do it quite independently — that is to say, 

 after they have parted from the common ancestral stock. 

 Now Mr Upton produces another fimbriate fossil; and, as 

 it happens, one not allied in a close degree to T. plicata 

 or T. fimbria. It belongs to what is known as the ciwvi- 

 frons group, the proposed genus Pseudoglossothyris. iMr 

 Upton calls this fossil T. galeiforiiiis, a form in which a 

 further development of the ciLi^oifrons sulcus is shown. 

 But in his fossil a fimbriate margin is produced, and the 

 au^ifrons sulcus has been partially obliterated, or has 

 not been developed (see later, note p. 262.) 



The point then about these fossils is this. T. plicata 

 and T. fimbria show by their characters that they had a 

 common but not very remote ancestor — one, say, in the 

 Ludwigian Age (early Inferior Oolite.) But this fimbriate 

 Pseudoglossothyris shows by its characters a different line 

 of development since it separated from the common stock. 

 Presumably its date of departure therefrom was earHer, and 

 a species of Harpoceratan Age (Upper Lias) gives possible 

 support to the idea that the time was quite an "Age" 

 earlier. t Yet in the course of its development this 



* B3' this term I mean the principle of separating the valves by marginal deposit 

 without adding to their superficial area, example Zcilleria Waltoni. 

 t Bajocian Mid-Cotteswolds, p. 447. 



