180 



ORGANIC REMAINS IN LIAS. 



shells. Univalve unchambered shells are not numerous in this for- 

 mation, but a great variety of bivalve shells occur in it. The gry- 

 phite {GryphcKa incurva), a deeply incurved bivalve shell, abounds so 

 much in some of the beds of lias, that in France it has received the 

 name of Calcaire a gryphites,^ Pentacrinites also abound in the 

 upper part of the lias ; and in conjunction with gryphites, and the 

 ammonites that have a ridge between two furrows round the back of 

 the shell, are characteristic of the lias formation. The pentacrinite 

 and encrinite were zoophytes with long articulated stems and branch- 

 es : in the encrinite the stem is round, in the pentacrinite pentagonal. 

 The annexed cut represents part of the branches or arms of the Bri- 

 arean pentacrinite. 



The most remarkable organic remains are, however, certain spe- 

 cies of fish, and vertebrated animals allied to the order of lizards : 

 the fossil fish are generally found in the middle of flattened balls of 

 limestone, in which the form of the body and the scales is often well 

 preserved. The saurian or lizard-shaped animals have left no trace 

 of the form of their bodies, except what can be ascertained from the 

 remaining skeletons. To the Rev. W. D. Conybeare we are indebted 

 for having determined the forms of two genera of these animals. The 

 ichthyosaurus, or fish-lizard, had a head resembling a dolphin more 

 than a lizard, and numerous conical teeth; the orbit of the eye is 

 uncommonly large. Some idea may be formed of the magnitude of 

 these animals, when I mention that the orbit of the eye in a head be- 

 longing to Mr. Johnson of Bristol, which I measured, was ten inches 

 long and seven broad : the orbit in another head, belonging to the 



* The Gryphgea incurva has not, that I know of, been found in England either 

 above or below the lias, and therefore may be regarded as alone characteristic of 

 this formation. These shells occur very abundantly, and are provincially called 

 Millers' Thumbs, 



