﻿Vol. 6 1.] SEQUENCE IJST THE BRISTOL AREA. 301 



valve : short mesial septum. Pedicle -valve : strong dental plates ; 

 mesial septum. Within the delthyrium, there is a distinct rostral 

 callus and a trace of syrinx. I have not as yet obtained un- 

 equivocal proof of the existence of a syrinx, but the presence of a 

 rostral callus is indisputable. 



The rostral callus and the mesial septum in the brachial valve, 

 from their resemblance to similar structures in Syringothyris cuspi- 

 data, seem to be sufficient reason for assigning our specimens to 

 the genus Syringothyris rather than to Spiriferina. 



From Spiriferina octopUcata our species differs in the presence 

 of: — (1) a rostral callus; (2) a mesial septum in the brachial 

 valve ; (3) much larger size and more numerous ribs ; (4) and the 

 ungrooved mesial fold. 



From Syringothyris cuspidata our species differs in the strong 

 and separate ribs, and also in the laminose ornament and the 

 narrower, more concave area. Prom Syringothyris distans it differs 

 in the absence of ribs on the fold, and in the sinus. 



Syringothyris cuspidata (Mart.). 



The typical form, which is characteristic of the top of Z 2 and C, 

 is well depicted in Davidson's ' Monogr. Brit. Foss. Brachiop.' 

 vol. ii (1858-63) pi. viii, figs. 21-23 (*■ Spirifera' cuspidata). 



Syringothyris aff. cuspidata, which is common from the top of 

 Kj to Z, is a smaller form, with lower cardinal area and a narrow 

 deep sinus which has, usually, tumid walls ; the ribs on the pedicle- 

 valve are broad and flat, and separated only by mere striae. 



The gens of Syringothyris cuspidata seems to be essentially 

 characteristic of the Tournaisian : it is abundantly represented 

 from the top of K x up to the top of C. It culminates in the very 

 large typical form that appears to indicate the end of its long- 

 line of evolution. The occurrence of this large typical form 

 seems consequently to mark a very definite and important datum- 

 level, which has a true evolutionary basis. 



Cyrtina. 



Cyrtina carbonaria (M'Coy). 



M'Coy, ' Brit. Palseoz. Foss.' 1851-55, p. 442 & pi. iii D, figs. 12-18 

 (Pentamerus carbonarius) ; Davidson, ' Monogr. Brit. Foss. Brachiop.' 

 vol. ii (1858-63) pi. xv, figs. 5-14. 



This species has not, as yet, 1 been definitely recognized in the 

 Bristol area, but in surrounding areas it is an important zonal fossil 

 and characterizes the Upper Seminula-Zone (Chepstow, Kidwelly, 

 Weston, and Tenby). 



Eumetria. 



Etjmetria spp. 



James Hall, ' Thirteenth Ann. Eep. State Geologist N. Y. (1893-94) : 

 Introd. to Study of the Brachiop.' pt. ii, p. 795 & pi. xxxvii, figs. 1-12. 

 Compare also Retzia carbonaria, Davidson, ' Monogr. Brit. Foss. 

 Brachiop.' vol. ii (1858-63) pi. Ii, fig. 3. 



1 See under Wickwar, p. 239, footnote. 



