Tol. 68.] SUCCESSION IN THE NORTH-WEST OE ENGLAND. 469 



(C) The Produdus corrugato-hemisphericus Zone.^ 



This zone is separated, for convenience of description, to include 

 a group of beds lying between the Miclielinia and the Dihuno- 

 pluillam Zones. The name of the index-fossil was origiually 

 suggested by Dr. Vaughan, and is adopted here as representing 

 the general type of Productus which is common throughout the 

 zone. The form is not absolutely confined to this zone, for occa- 

 sional specimens are met with in the upper portion of the underlying 

 Miclielinia Zone. There is no one species that can be cited as 

 confined to the zone, and yet as characteristic of it throughout. 

 This zone marks the passage between the lagoon and shallow-water 

 phases characteristic of the beds of the lower zones and the clear 

 and deeper-water conditions Avdiich obtained during the deposition 

 of the beds of the overlying Lower Dihunophijllum Sub-zone. The 

 fauna is also intermediate in character. The zone is present in all 

 the districts, and maybe subdivided as follows : — 



Upper —Lithostrotion (Nematop]iyllum.)-minus Eeds. 

 Middle = Cijrtina-carbonaria Beds. 

 Lower ~ Gastropod Beds. 



[e) The Gastropod Beds. 



This sub-zone contains no one species that can be cited as an 

 index, but is usually characterized by a rich assemblage of gas- 

 tropods and other mollusca, such as BelleropJion, Euomplialus, etc. 



Lithology. — The lower portion is a dark bituminous, somewhat 

 shaly limestone, which in the Arnside and Grange districts passes 

 gradually down into the underlying Miclielinia Beds. In the 

 districts where the Cyrthia-carhonaria Sab-zone is absent, the 

 black limestone-beds are succeeded somewhat abruptly by the over- 

 lying compact white limestones of the Nematoj)hyTlum-minus 

 Sub-zone. 



Pa una. — In the Western Districts these beds contain many 

 species in common with those of the underlying MicJieliaia Zone, 

 but Midielinia and Chonetcs carinata are absent. Litliostrotion is 

 associated with Belleroplion and Euomphalus. Semiuula occurs 

 abundantly near the base, together with a large form of Diphy- 

 phylloid Lidiostrotion. A similar fauna, including the same Diphy- 

 phylloid Litliostrotion, is found in the Havcnstonedale District. The 

 fauna of the calcareous band which occurs in the Ashfell Sandstone 

 of the latter district is, however, unique in the area, being rich 

 in corals, especially in forms of Lopliopliyllum ashfellense and 

 specimens of Zaplwentis ennisldllenl and variants. 



1 This zone appears to represent abuost exactly the Scminula Zone of the 

 Avon Section. The index-fossil is described and iigured by Dr. Vauj^han as 

 Producius com, nint. S,, in Q. J. G. S. vol. Ixi (1005) p. 291 & pi. xxv, lig. 4. 



