EXPLANATION OF THE PLATES. 



Plate XIV. 



Fig. 1. Section of the coast of Dorset, from Lyme Regis to the Isle of Portland, as 

 seen from Lyme Regis ; showing the manner in which the valleys are intersected 

 at the point where they are terminated by the present sea shore. It is probable 

 that a considerable portion of this coast has been worn away by the sea, and that 

 the small clay valleys or combes, which are now abruptly truncated at their ter- 

 mination, Avere originally continued with a gradual slope to the water's edge. 

 The form of these cliffs and of those represented in fig. 2, as seen from a boat 

 in passing along the coast, is represented in the sections by Mr. De la Beche, 

 Plate VIII. of the present volume. 



Fig. 2. Section of the coast of Devonshire, from Sidmouth to Beer-head. The first 

 combe or dry valley, on the E. of Sidmouth, is abruptly truncated, like those 

 represented in fig. 1. ; the others terminate by a gradual slope in the sea. The 

 line of junction of the green sand with the red marl is marked by the termination 

 of inclosures and of fertile soil, exactly at the point where the green sand begins. 

 The table lands that form the summits of these green sand hills are for the most 

 part barren heaths, except where they are covered with diluvian gravel, or by a 

 bed of unrolled chalk flints. This observation applies also to the green sand 

 summits in fig. 1, — and to the table lands composed of the same stratum, which 

 stretch inland from the coast to the flat summits of the Black Down hills, — in 

 which this formation attains its highest elevation, overhanging with its escarp- 

 ment the vale of Taunton. 



PLATES XV. XVL XVIL XVIIL XIX. XX. XXI. & XXII. 



Illustrate the Rev. Mr. Conybeare's additional Notices on the fossil Genera Ichthyo- 

 saurus and Plesiosaurus, Article IX. p. 103. 



General Letters of Reference. 



Throughout the series of plates illustrating the former* and the present Memoirs 

 on the genera Ichthyosaurus and Plesiosaurus, the same letters have been employed 

 in reference to the sevei-al bones which compose the skeleton of the head ; being those 

 previously applied in a similar manner to the osteology of the Crocodile's head by 

 M. Cuvier. It may be convenient to the reader to have these references at once un- 

 der his eye : the author has therefore added the whole alphabetical series, — although 

 some of the bones, designated by particular letters, . are not visible in the present 

 plates, — with the intention of continuing the same references in any future plates of 

 the heads of other sanrian animals ; which will secure the double advantage of mak- 

 ing the present list a complete index to the osteology of the head in the genera of this 

 order, and of rendering any future table of reference unnecessary. The bones not 



* Geological TransactioHS, Vol. V, p. 559. 



