﻿Vol. 6r.] 



SEQUENCE IN THE BEISXOL AREA. 



297 



the dimensions of the Bristol specimens are considerably less than 

 those of Davidson's figures. 



Hhipidomella. 



Khipidomella Michelini (L'Eveille), Davidson. 



Davidson, 'Monogr. Brit. Foss. Brachiop.' vol. ii (1858-63) pi. xxx, 

 figs. 6-8 {Orthis Michelini). 



[A species of Mhipidomella, with strongly-marked beak and hinge- 

 area, which bears a strong resemblance to Rh. Michelini, occurs very 

 rarely in e.] 



Cliothyris. 

 Cliotbtbis Royssii (L'Eveille). 



Fig. 8, Davidson, op. cit. pi. xviii {Athyris lioyssii), represents the typical 

 form and ornament. 



Cliothyris Royssii mut. /3 is described and figured in Vaughan, 

 Proc. Bristol Nat. Soc. n. s. vol. x (1903) p. 124 & pi. ii, fig. 2. 



This mutation is a more globose shell, usually of smaller size, 

 with a broader beak and a larger perforation. It occurs most 

 abundantly at a higher horizon than the typical form, but is 

 connected with that form by a perfectly -continuous series of 

 intermediate stages. 



Cliothieis glabkistkia (Phil.). (Text-fig. 5.) 



The general form is represented in Davidson, op. supra cit. pi. xviii, fig. 1 

 {Athyris Boyssii). 



This Athyrid is distinct, both in form and dimensions, from 

 the typical Cliothyris Royssii, and it occurs, moreover, at a higher 



level, being especially 

 Fig. 5. — Cast of pedicle-valve of characteristic of the 



Cliothyris giabristria. Zaphrentis-Zorie. 



Cliothyris giabristria 

 has,untilnow,been re- 

 corded from theBristol 

 area as * Spirifera ' 

 glabra, and it is ex- 

 tremely difficult, when 

 the beak-region is 

 obscured and the 

 fringes are absent, to 

 distinguish the two 

 species one from the 

 other by external 

 characters alone. 



The internal cha- 

 racters arc, however, 

 completely distinct: — 

 A Martinia, of 

 which genus the true Spirifer glaber is the type, has no dental 

 plates and inconspicuous muscular scars. 



a — Adductors. o = Ovarian markings. 

 v — Diductors. d — Walls of pedicle- ■ 

 cavity formed by the dental plates. 



