LIASSIC FORMATIONS. 119 



of the general description of the cranial organisation of the genus differ in the specific 

 modifications referred to in other sections of the present Monograph. 



From the Upper Lias, with remains of Ammonites bifrons, of the Cotteswold Hills. 

 The more complete cranial specimen from the same Liassic zone at Curcy, Normandy, 

 has afforded the subjects of the figures in the plates above cited. 



g. Ichthyosaurus latifrons, Km. PI. XXIII, fig. 6 ; PI. XXVII, fig. 1. 



In the year 1825 Mr. Konig, Keeper of the Department of Mineralogy, British 

 Museum, published a series of lithographs of fossils, in a folio form, with brief notices of 

 the subjects, reaching to number 100. Beyond this, names alone are given at the foot of 

 each plate, and No. 250 of plate xix bears that of Ichthyosaurus latifrons. It is a very 

 reduced view of a mutilated skull and portion of the vertebral column, with some vertebrae 

 outlined of the natural size. The specimen is stated to have been obtained from Lyme 

 Regis. 



Of this specimen a view of the upper surface of the skull is here given of the 

 natural size, in PI. XXVII, fig. 1. The upper apertures of the temporal fossae (r, t) are 

 nearly equilaterally triangular in form, the base being external and slightly exceeding the 

 sides, which converge to the cranium proper. The sagittal suture (7) persists, but the 

 frontal one is obliterated, and the midfrontals (n) constitute a single symmetrical bone, 

 which is moderately convex both lengthwise and crosswise. 



The " foramen parietale," of a full ovate figure, is formed wholly by the frontal, the 

 apex alone forming the beginning of the parietal suture. 



The postfrontal (12) extends upon the coronal suture, and overlaps part of both 

 parietal and frontal bones. The nasal (15) overlaps the fore part of the frontal, and 

 divides that bone from the prefrontal (14). The sides of the skull converge rapidly to 

 the beginning of the snout. A breadth of cranium across the temporal apertures of 

 7 inches is reduced to 2 inches anterior to the nostrils (ib, n). 



Additional characters of the present species are afforded by a second specimen from 

 Lyme Regis acquired by the British Museum. It is a skeleton, lacking both ends, but 

 including the trunk, with chief part of the skull and basal portion of the tail, the total 

 length being 4 feet 10 inches. From the occipital condyle to the pelvis it measures 

 2 feet 6 inches ; the length of the preserved portion of the skull is 1 foot 4 inches. In 

 this specimen is instructively shown the sudden slope by which the broad cranium 

 descends into the rostrum. The orbit is correspondingly large, its vertical diameter is 

 5 inches, its antero-posterior one is 4^ inches. The sclerosteal circle is composed of 

 correspondingly large plates, of which seven are preserved. 



