112 
FOSSIL REPTILIA OF THE 
The midfrontals tahe the chief share in the formation of the parietal foramen, and 
are excluded from the upper border of the orbit by the pre- and postfrontals. The 
sclerotic plates are sixteen or seventeen in number. 
The nostril is bounded by a straight line above, contributed by the nasal bone, and 
by a curved line below, due to the lacrymal and premaxillary. The maxillary is 
excluded from that opening ; it receives the pointed fore end of the malar in a notch ; that 
slender bone forms the whole of the inferior border of the orbit. 
In the mandible the surangular extends forward beyond the angular. The dentary 
elements unite to form the major part of the symphysis, a small hind portion being 
contributed by the splenials (PI. XXX, fig. 4, 32')- The symphysis so constituted had, 
in a lower jaw 2 feet 9 inches in length, an extent of 9 inches. 
The vertebrae are shorter, or their centrums have a minor antero-posterior extent in 
proportion to their breadth, than in some other species {Ich. intermedins, Ich. latimanus, 
e.gi), but are longer than in Ich. hrachyspondylus. I have counted forty vertebrae between 
the occiput and the “ sacrum,” conventionally so calling the centrum nearest the iliac 
bones. From this to the end of the tail follow, at least, one hundred vertebrae, of which 
seventy-five no longer support pleurapophyses. The total number of vertebrae in Ichthyo- 
saurus communis may be set down at 140. 
The episternuui shows no marked specific character. The coracoids have the anterior 
notch deeper than the posterior one (PI. XXX, fig. 3). The clavicles are long and 
strong, applied, as usual, to the fore border of the transverse rays of the episternum and 
to that of the scapulae. 
The bones of both fore and hind paddles have afforded the description given in the 
preliminary general account of the Ichthyosaurian skeleton (p. 104). 
In the specimen (PI. XXX, fig. 3), in which the pelvic arch and limb are unusually 
well preserved, the ilium (ib. figs. 5, 62 ) is sabre-shaped or moderately curved backwards ; 
in length 2^ inches, with a breadth of 5 lines at the middle. The pubis ( 64 ) of the same 
pelvis is 2 inches 9 lines in length, 1 inch in distal breadth ; both fore and hind borders 
are concave. The ischium ( 63 ) is nearly of the same length as the pubis, with a distal 
breadth of 9 lines, and a deeper concavity of the anterior border. The entire vertical 
extent of the pelvis is 5 inches. 
The length of the pelvic paddle in the subject of fig. 1, Pi. XXXIII, is 4| inches; 
that of the femur being 1 inch 7 lines. The extreme breadth of the paddle is 1 inch 
10 lines. At this part there are five phalanges in transverse line, that number occurring 
at the fifth bone from the femur. The midtarsal encroaches further between the tibia 
and fibula than usual. 
The Ichthyosaurus communis occurs chiefly in the Lias of Lyme Regis and Charmouth, 
Dorsetshire ; in that of Street, Somersetshire, it is rarer than the Ichthyosaurus inter- 
medius. Remains of Ichthyosaurus communis have been met with in the Lias near 
Bristol. This species is associated with Ich. intermedius and Ich. tenuirostris in the Lias 
