546 MR. E. E. L. DIXON AND DR. A. VAUGHAN ON [Nov. I9T I, 



Syringothyris Zone (C). 



Eastern District: ThreeclifF Bay (4) and Longland Bay (6). 

 South- Western District : — Cliff west of Overton. 



Ci: 



Composed of the laminosa dolomite and Caninia-Oolite. 



Fossils are very scarce ; narrow-tubed Syringopora, large-celled 

 Michelinia, small Zaphrentis, large Caninia, and an early Clisio- 

 phyllid were, however, recorded from various places in Eastern and 

 South-Western Gower, as well as a band of Chonetes cf. comoides 

 and of Belle rophon in the Caninia Oolite of Longland Bay. 



C 2 : 



Lowest part of the standard limestones. 



Zaphrentis omaliusi Ed. & H., Carruthers — 4 and 6. 



Zaphrentis koninchi Ed. & H., Carruthers — 4 and 6. 



Caninia cylindrica (Scouler in M'Coy) Vaughan — abundant in 4. 



Syringothyris cuspidata (Martin) — 4 and 6. 



Syringothyris cf. laminosa Vaughan— rare in 4 and 6. 



CyathophyUum Vaughan (small mut, 1 ) — 4 and 6. 



UPPER AVONIAN. 2 



C 2 : 



Main part of the standard limestones. 



Corals : — 



Syringopora cf. genieulata Phill., Nicholson — 4 and 6. 



Syringopora cf. reticulata—^. 



Michelinia grandis' 6 M'Coy — 4 and 6. 



Zaphrentis konincki, mut. C 2 4 — 6 (nearly at the top). 



Caninia cylindrica (Scouler in M'Coy) Vaughan — 4 and 6. 



CyathophyUum <p Vaughan— abundant in 4 and 6. 



Diphyphylloid Lithostrotion — Overton. 



Brachiopods : — 



Chonetes cf. comoides (Sow.). 

 Hhipidomella aff. michelini — 6. 

 Spirifer cf. trigonalis 5 — 6. 

 Syringothyris cuspidata — 4 and 6. 

 Semimila sp. 6 [cf. S. ambigua (Sow.)] — 6. 



i CyathophyUum $ is not established until C 2 ; the small mutation is, there- 

 fore, a descending mutation, that is, a previously established member of the 

 gens. It obeys the general law — ' earlier and smaller.' 



2 The reasons for starting the Upper Avonian at this level are set out in § VI. 



3 — Michelinia. cf. megastoma of my earlier lists. 



4 Zaphrentis konincki is a Z 2 to y index ; this mutation is, therefore, an 

 ascending mutation : that is, a subsequently-established member of the gens. It 

 is larger, and has longer intermediates, in accordance with the general rule. 

 [See my note in E. Q. Carruthers's paper, Geol. Mag. dec. 5, vol. v (1908) p. 70.] 



5 Small, sharply-ribbed form with a strong angular fold, somewl at produced. 



6 Deeply sinuate form, recorded as Seniinula, ambigua by Dr. T. F. Sibly, 

 from Weston and the Mendips. 



5 & 6 These forms characterize the C-S level at widely separate localities 

 in England ; they are, therefore, important diagnostic forms. 



