LIASSIC FORMATIONS. 
123 
seems to be rather longer, proportionately, than usual : in the subject of fig. 2 it is 
2^ inches in length. 
In the composition of the lower jaw, I have noted that the angular element extends a 
short way in advance of the surangular before disappearing externally. Tlie point of 
the surangular enters a notch in the hind part of the dentary, about half an inch 
anterior to a line dropped from the fore part of the nostril. The angular disappears, as 
usual, between the splenial and dentary, not between the splenial and surangular. The 
splenials contribute a small proportion to the mandibular symphysis (PL XXV, fig. 3, 32 '). 
The teeth (PI. XXIV, fig. 8) conform in relative size and slenderness of crown with 
the slenderness of the bones wielding them. Those at the fore half of the jaws incline 
more backward than usual, and hardly assume a vertical position in the maxillary and 
post-mandibular regions. I have counted from sixty-five to seventy on each side of the 
upper jaw, of wdiich twenty-five, or thereabouts, are implanted in the maxillary. In the 
lower jaw there are about sixty teeth in each dentary (PL XXXII, fig. 2, 33). A few 
detached teeth in a portion of a large Ich. temdrostris from the Lias at Pyx Hill measure, 
each, 1 inch 4 lines, the enamelled crown being about a third of that length ; tlie cement- 
clad root is 4 lines in diameter, rather thicker in proportion than in the smaller-sized 
specimens of the present species. 
The vertebral column (PL XXXII, fig. 1) agrees in general length with the charac- 
teristic shape of the head. In the best preserved specimens it is nearly four times the 
length of the skull. 
I have counted 156 vertebras in a well-preserved column of the large specimen from 
Pyx Hill ; in this the pinnigerous part of the tail was twm feet in length, and had been 
bent down in the burial and subsequent petrifaction of the Sea-dragon at almost a right 
angle to the trunk; this deflected part included sixty centrums, which seemed to be 
relatively somewhat shorter as well as narrower than those of the trunk. At the bent 
part of the column the margins of the terminal articular facets were slightly deflected, 
and markedly raised from the level of the sides of the centrum, indicative of the degree 
and frequency of flexure at this part. The fore-and-aft diameter of a post-abdominal 
vertebra in an average-sized Tennirostral is 13 lines, the vertical diameter being 2 inches 
6 lines. The terminal articular surfaces of the centrums are more uniformly concave 
than in the previously described species. I have not found in Ich. temdrostris more than 
two hypapophyses at the fore part of the column, one wedged between the basioccipital 
and the atlas, the other between the atlas and axis. This more simple apparatus for fixing 
the immediate support of the skull suggests an accordance with the lighter and more 
slender character of that part. The centrums gradually increase in fore-and-aft dimen- 
sions to the pelvic region, and do not begin to decrease in size till about ten vertebrae 
beyond the part forming the base of the long caudal region. 
The ribs soon become long and slender as they recede from the head, and increase in 
length to near the hind end of the abdomen ; thence they shorten less gradually than 
17 
