﻿260 DK. A. VAUGHAN ON THE PAL^ONTOLOGICAL [May I905, 



The index-fossil is subject to small geographical variation, but is 

 widely distributed (Bristol, Mendips, Forest of Dean, Tenby), and 

 I have not myself found it outside its own subzone. 



The octoplicata-suhzone contains : — 



(1) The early representatives of the Zaphrentis-f&unsi, which 



become more and more numerous in species and indi- 

 viduals, until at Horizon /3 a characteristic Zaphrentis- 

 facies is developed. 



(2) Yery few characteristic forms ; the maxima of Cleistopora 



and of Spiriferina octoplicata, however, fall within this 

 subzone. 



The Zaphrentis-Zone. 



This zone witnesses faunal changes of the greatest importance. 



(1) At the base Zaphrentids enter ; in the upper part the 



typical Zaphrentis-group becomes the dominant faunal 

 factor ; and at the very top of the zone the Caninia- 

 group is evolved from a Zaphrentis-ancestor. 



(2) This zone includes the maximum development of the 



Orthids. 



(3) Starting with the maximum of Spirifer, it ends with that 



of Syringothyris. 



(4) The zone witnesses the mutational change of the small 



Productus cf . Martini into the typical Pr. semireticulalus . 



(5) At the top of the zone, Chonetes papilionacea supplants 



Ch. cf. hardrensis as the dominant Chonetes. 



(6) A characteristic fish-fauna is developed (see above, p. 253). 



The clathratus- and resupinata-suhzoiaes. 



Whereas the clathratus-suhzone exhibits a direct continuity 

 and expansion of the Cleistojoora-iaxma, the resupinata-suh- 

 zone witnesses the introduction of the Jam inosa-f a,unai (Caninia, 

 Syringoihyris aff. laminosa). The resupinata-suhzoris is well cha- 

 racterized by containing the maxima of Zaphrentis, Schizophoria 

 resupinata, and Cliothyris glabristria. 



The Caninia-Zone. 



If we adhere to a coral-basis for zonal division, Caninia is the 

 only possible index that can be selected to succeed that of 

 Zaphrentis; and, although I have ultimately decided to relegate this 

 index to a secondary place, it has undoubtedly a very considerable 

 value, both from the point of view of field-work and from an 

 evolutionary standpoint. 



The displacement of Caninia is based on the following con- 

 siderations : — 



(1) When measured against the brachiopod-progression, the range of Caninia 

 does not cover the same terms at different poiuts of the Bristol area, as already 

 pointed out (p. 185). 



