410 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Feb. 29, 



The Zone oe Ammonites Btjcklandi is remarkable for containing 

 a great number of large Ammonites belonging to Yon Buch's group 

 Arietes, such as Am. BucMandi, Am. rotiformis, Am. Conybeari, Am. 

 angulatus, &c, -which everywhere characterize this stage where it is 

 developed in Europe. Saurian remains are not so abundant in this 

 as in the Am. planorbis zone ; but Lima gigantea, L. antiquata, and 

 other congeneric forms, with Gryphaza arcuata, prevail in abun- 

 dance throughout. In the uppermost beds only Belemnites acutus 

 occurs, and that in small numbers. 



The Zone oe Ammonites Turneri is characterized by the appear- 

 ance of several species of Ammonites, as Am. Turneri and Am. semi- 

 costatus, and the abundance of a remarkable crinoid, Pentacrinus 

 tubercidatus, Mill. The Ammonites which prevailed in the Am. 

 BucMandi zone are mostly all absent from this. The second Lias 

 Saurian zone belongs to this subdivision, for the beds richest in 

 remains of Fish and Sanrians at Lyme Regis (containing Ichthyo- 

 saurus platyodon, I. intermedins, and i". communis) belong to the 

 zone of Am. Turneri. Unfortunately the beds yielding the different 

 species of fossil Fishes have not been noted with sufficient accuracy 

 to enable me to state what species belong in particular to these bee's. 



The Zone oe Ammonites obteses contains many species of Am- 

 monites which here appear for the first time. Ammonites obtusus, 

 Am. Birchii, Am. Brookii, Am. Smithii, Am. Dudressieri, and Am. 

 planicosta, with Nautilus striatus and Belemnites acutus, form the 

 group of Cephalopoda here. Saurian bones occur sparingly in these 

 beds ; and a remarkable thin bed of limestone, characterized by im- 

 mense numbers of Extracrinus Briareus which are preserved on the 

 surface of the slabs, belongs to this zone. 



The Zone oe Ammonites oxynotus contains three or four species of 

 Ammonites which have a very limited range in time, as Ammonites 

 oxynotus, Am. bifer, and Am. lacunatus ; with a number of small 

 Conchifera belonging to the genera Area, Leda, Astarte ; and small 

 Urchins, as Acrosalenia minuta, and fragments of Crinoids. 



The Zone oe Ammonites raricostates possesses a remarkable 

 assemblage of Mollusca. The Ammonites are all special to this zone: 

 of these, Am. raricostatus, Am. armatus, Am. densinodus, Am. nodu- 

 losus, and Am. Guibalianus are the most abundant. Cardinia Listeri 

 is found in great numbers, with Gryphcea obliquata and Hippopo- 

 dium ponderosum, together with a thin band of small Corals, and 

 Belemnites acutus. The clays forming this zone and that of Am. oxy- 

 notus are largely charged with the sulphuret of iron, and hkewise 

 with the peroxides of that metal, so much so that the fine fossils 

 found therein fall to pieces in the bed, or rapidly decompose when 

 exposed to the atmosphere. 



The following Table shows at one view the geographical distribu- 

 tion of the different zones of the Lower Lias. 



