232 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
produced into lobes an inch in length, aa. The lateral edges are less 
obliquely truncated than in the second segment. 
4th Segment—Wanting in our plate; it is the largest and broadest 
of all in the Tealing specimen (woodcut 9); its sides are less oblique 
than in the third segment. 
5th Segment, Plate IV. [Plate 15] fig. 2—Fully five times as 
broad as long, the sides are nearly rectangular, not oblique, the 
posterior angles very little rounded, the anterior not (?) produced. 
Our largest specimen measures more than a foot wide and two 
inches and a half long. 
6th Segment, Plate 1V. [Plate 15] fig. 3—-Of the same shape as 
the fifth, but only four times as broad as long. 
Of the remaining rings, figs. 5, 6 show imperfect fragments. 
They gradually taper backwards, as indicated by the dotted margins, 
and become thus narrower in proportion to their length, but exhibit 
no other difference, as we learn from the above perfect specimens, as 
far as the ninth. 
Plate V. [Plate 16] fig. 1, can scarcely be any but the tenth 
segment. It is about once and a quarter as wide as long, the sides 
straight, and the posterior angles a little produced. 
The 112k segment, figs. 3, 4, suddenly changes shape, it is half 
oval, with both ends truncate, and its length is rather more than 
three-fourths of the width. The base is contracted, the sides curve 
boldly outwards, and again contract at the produced and hooked 
posterior angles. The segment is thus much broadest behind. We 
have both upper and under surfaces, the former is carinated all the 
way down by a strong median ridge, wider and less prominent at 
first, then sharply elevated and covered with coarse squame. The 
under side, fig. 3 6, has no median ridge except for its middle 
third, and this, which begins by a gentle elevation, ends abruptly 
rather more than two-thirds down. It is closely covered with large 
squame, and probably indicates the place of the anal opening. The 
lateral and posterior margins are also bordered with tubercular 
squame, largest and most conspicuous on the sides. Our finest 
specimen is three inches and three-quarters long, and four inches 
and a quarter wide behind the middle, where the width is greatest ; 
at its upper end it is only two inches and a quarter broad. 
In the same beds, near Forfar, penultimate joints occur, which 
are probably of the same species, but show a marked difference 
from those in the plate. An upper and under side is here figured. 
The former is destitute of any carina; on the latter an abbreviated 
(anal?) ridge exists, but on the posterior third only (exactly as in 
