112 FOSSIL REPTILIA OF THE 



The midfrontals take 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 vertebras 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.y.),hv\t are longer than in Ich. brachyspondylus. I have counted forty vertebra? 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 vertebras in Ichthyo- 

 saurus communis may be set down at 140. 



The episternum shows no marked specific character. Thecoracoids 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- 

 medins. Remains of Ichthyosaurus communis have been met with in the Lias near 

 Bristol. This species is associated with Ich. intermedins and Ich. tenuirostris in the Lias 



