KIMMERIDGIAN PLIOSAURS. 159 



marked angular coronoid process. Anterior to tliis tlie upper border of the 

 mandible becomes tliick and transversely convex; and, an inch below tbe 

 border, the outer side of the ramus is impressed by a wide and deep longitudinal 

 groove. So much of the articular surface as is preserved agrees in structure and 

 form with that in Plioscairus grandis ; and the extent of the angular projection 

 behind the articular cavity to the same. 



The fore part of the symphysis, including the first three pairs of teeth, restored 

 in PI. 19, fig. 4, has been subject to such violent horizontal force as to be crushed 

 in that direction, and broken across both the upper and the under surfaces of the 

 rest of the mandible, without having been detached from the intervening structure 

 or tissue of the bone. The bottoms of the sockets only of the included teeth are 

 preserved, with parts of the partitions which, here, are only from 2 to 3 lines thick. 

 These sockets increase in size to the third. The diameter of the outlet of the 

 fifth socket, which is the first entire one, measures 1 inch 9 lines across ; it is 

 rather less longitudinally. The outlets of most of the alveoli are subcircular, with 

 a tendency to a subquadrate section, with intervals not exceeding 2 lines, and they 

 retain a uniformity of size to within four or five sockets at the end of the series, 

 which progressively decrease in size. 



The total number of teeth, as shown by sockets, in each mandibular ramus, is 

 fourteen ; of which ten occupy the symphysial part of the jaw. 



The upper surface of the symphysis between the first six teeth is flush with the 

 alveolar outlets, is smooth, and slightly convex transversely. Beyond the sixth 

 pair of teeth the intervening surface rises above the inner borders of the alveoli as 

 high as half an inch between the ninth — eleventh pairs of sockets ; the upper 

 surface of the hinder part of the symphysis becomes slightly convex transversely, 

 and the pointed anterior ends of the splenials (si) enter into its composition. 



No part of the upper jaws of this skull of PUosaurus troclianterius has been 

 preserved; but the quarrymen extracted the hind part of the cranium (PL 19, 

 fig. 6). It shows a hemispheroid condyle (1) 2 inches 8 lines in basal diameter. 

 The foramen magnum is a full transverse ellipse, 1 inch 3 lines across. The broad 

 and low occipital surface includes the thick horizontal backwardly projecting 

 paroccipital ridges (4), below which extend still more backward and somewhat 

 downward the short and broad tympanies, terminated each by a condyle convex in 

 its outer two thirds, concave transversely at the inner third : the breadth of this 

 condyle (28) is 5 inches. 



The upper transverse ridge of the occiput is broken away. The parietal 

 region (7) is formed by a lofty median vertical wall of bone, slightly expanding 

 below to form the side walls of a miserably small cerebral cavity. 



I have neither respect nor inclination for undue multiplication of genera ; but 

 the degree of difference in the number of mandibular teeth and extent of the 



