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 hifrons, of the Cotteswold Hills. 
The more complete cranial specimen from the same Liassic zone at Ciircy, Normandy, 
has afforded the subjects of the figures in the plates above cited. 
Ichthyosaurus latifrons, Kon. PI. XXIII, fig. 6; PL XXVII, fig. 1. 
In the year 18.25 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 Icldhyosaiirus 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 (ii) 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, »*). 
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. 
