ZONE OF AEGOCERAS PLANORBIS. 



23 



It is likewise found at Robin Hood's Bay, on the coast of Yorkshire ; the beds lie 

 here below low-water mark, and large blocks, frequently washed up by the tide, are literally 

 crowded with Aegoceras planorbis, known at Scarborough and Whitby as Aeg. erugatum, 

 Bean. 



The Coral-bed at Lussay, Isle of Skye, 1 probably represents this zone, as I found the 

 same species of Anthozoa as the Hebridean Coral Isastraa Murchisoni, Wrt., in the light- 

 coloured clays with Aeg. planorbis at Street. 



This lower Ammonite-zone has, therefore, a wide geographical range through- 

 out the Lower Lias of the northern, midland, and southern counties of England, and 

 retains the same relative position in the Lower Lias of France, Germany, and 

 Switzerland. 



The detailed sections which I have given of the Planorbis-zone form some of the best 

 known types of the basement-beds of the Lias in England, and enable us to understand 

 their relations to the Contort A-series below, and the ANGULATUM-strata which succeed 

 them. 



Fossils of the Planorbis-beds. — The fauna of this zone is very limited ; at present I 

 know only the following species from the English beds : 



Ichthyosaurus intermedius, Conyb. 



— tenuirostris, Conyb. 



— communis, Conyb. 

 Plesiosaurus Hawkinsii, Conyb. 



— Etheridgii, Hnxl. 



— rugosus, Owen. 



— dolichodeirus, Conyb. 



— megacephalus, Stutch. 

 Dapedius, sp. ined. 

 Pholidophorus leptocephalus, Ay. 



— Stricklandi, Ag. 



Aegoceras planorbis, Sow. 

 — Johnstoni, Sow. 

 Lima punctata, Sow. 



Lima gigantea, Sow. 

 — pectinoides, Sow. 

 Cardinia crassinscula, Sow. 

 Unicardium cardioides, Phil. 

 Ostrea liassica, Stride. 

 Protocardia Phillipsiana, Dukr. 

 Pleuromya Crowcombeia, Moore. 

 Rhynchonella variabilis, Schloth. 

 Cidaris Edwardsii, Wrt. 

 Pseudodiadema lobatum, Wrt. 

 Hemipedina Bechei, Brod. 



— Bowerbankii, Wrt. 



Hemipedina Tomesii, Wrt. 

 Isastrcea Murchisoni, Wrt. 



Foreign Correlations. — In the North of Germany the PLANORBis-beds are well 

 developed, and in some parts contain a Flora in which are found many species that 

 appeared for the first time in the CoNTORTA-zone; the most important genera are Equise- 

 turn, Dictyophylltcm, Clat/iropteris, Glossopteris, Tceniopteris, Pterophyllum, Zamites, 

 Nilssonia, and many others. 



The Molluscan fauna contains many species which are common to this and the 

 Angulatum beds; the following species were nearly all collected at Halberstadt, and 



i t 



Quart. Journ. Geol. Soc.,' vol. xiv, pp. 4 and 34. 



