LIASSIC FORMATIONS. 
115 
The present species has afforded the chief ground of the restoration outlined in fig. 1 ^ 
PI. XXXIIJ. The humerus is marked 53 ; the radius 54 ; the ulna 55 . The fore 
border of the radius is entire, not notched. The antibrachium supports, as usual, three 
ossicles (56), followed by four rather smaller ( 56 ')- Regarding these as carpals, they 
support four metacarpal ossicles (57—57'), from which are continued five longitudinal 
series of progressively diminishing phalanges. The anterior or radial metacarpal (57) 
supports two digits, of which the radial may be symbolised as I, the next series as 
digit II. The three other series. III, IV, V, are supported by their respective meta- 
carpals. Each digit consists of numerous phalanges, progressively decreasing to the end. 
A series of small supplementary ossicles is applied to the radial border of digit I, and to 
the ulnar border of the digit V, so that seven ossicles may be counted in the same 
transverse line along the middle third or fourth of the series. The number of phalanges 
is, however, less than in Ich. commimis, and the fin is relatively narrower. The characters 
of the fore paddle above defined are well shown in specimens from the Lias of Lyme 
Regis and of Street, in the British Museum. 
In the pelvic fin the femuris longer in proportion to its breadth, and the distal 
expansion is relatively greater than in the humerus. The tibial ossicle of the three 
tarsals has an emarginate tibial border ; the corresponding ossicle or phalanx of the 
second and third series shows the same character. 
d. Ichthyosaurus platyodon, Cb. Plate XXIV, figs. 4 , 4 ' ; PL XXXI, figs. I, 2 , 3 . 
The skull of Ichthyosaurus platyodoii (PI. XXXI, fig. 2 ), is somewhat longer in 
proportion to the trunk than in Ich. communis. Taking as the trunk the extent of the 
vertebral column to the pelvic arch, such extent includes, in the subject of fig. 1 , one 
length and a half of the skull, while in Ich. communis (PI. XXVIII, fig, I) it includes 
rather less than two lengths, and, in Ich. intermedins (PI. XXX, fig. 1 ) rather more. 
The skull of /c/<. is longer in proportion to its breadth than in Ich. inter- 
medius. The jaws are stronger from the greater relative depth of the mandible and 
the less gradual attenuation to the rostral extremity. The orbit is of a full elliptic 
shape, with less approach to the circular, than in Ich. hrevicejos (PI. XXIX, fig. 1 ). It 
is relatively less than in the long- and slender-snouted kinds. The length of the rostrum 
anterior to the orbit is three and a half times the longitudinal diameter of that cavity. 
The osseous circumpupillary ring includes thirteen sclerotic plates in the subject of 
PI. XXXI, fig. 2 . The surangular (PI. XXXI, fig. 2 , 30) disappears between the 
dentary (33) and angular (31), This element similarly disappears in a pointed form 
between the dentary (33) and splenial (32), beyond the midlength of the ramus. 
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