254 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
PLaTE NIII. [PLaTE 24] Fics. 8, 12, 13, 15, AND 16. 
PTERYGOTUS ARCUATUS. 
Spec. CHar. PP. mayor, segmentis arcuatis, plicts semicircularibus parvts, 
nec squamults minutioribus tntermixtis. 
The name is applied to a large and fine species, of which several 
fragments occur in the Lower Ludlow Rock of Leintwardine, along 
with the more common P. functatis, Plates X., XI. [Plates 21, 22]. 
It is clearly distinct from that species, but except for the total absence 
of any minute interspersed plice, the body segments might be easily 
mistaken for those of P. problematicus, to which it is closely allied ; 
and with it, in the same beds of Lower Ludlow Rock, occur antenne 
(fig. 8), the obscure appendages (fig. 16), swimming feet, maxillz, 
and other oral apparatus, differing specifically from those of P. prob- 
Zematicus, and yet more distinctly separated from the portions of 
P. punctatus, found in the same beds. Of these fragments the body 
segment must receive the name, the other pieces being only pro- 
visionally arranged with it. They all resemble the corresponding 
parts in the Upper Ludlow species. 
Body Segments.—Fig. 12 is clearly, from its shape, the second 
body segment, seven inches broad and more than one inch and a 
half deep. It is curved, and more oblique laterally than in P. anglicus, 
the sides forming an angle of 65° with the base. The anterior 
edge is much more sinuated than the posterior, owing to the deep 
excavation to receive the first segment; but the central part is 
strongly arched forward on both margins. The lateral anterior 
process a is broken off, but enough remains to show it was pro- 
minent. The sides are oblique, inclined forward at an angle of 80° 
from the posterior angle, which is rounded off. The margin is 
crenulated, the prominent minute sculpture confined to the anterior 
third, but continued more faintly over a large part of the segment. 
(The sculpture in the thoracic segments of P. punctatus, Plate N. 
[Plate 21], though not carried over a much larger part of the 
surface, is far more prominent and remote.) 
A specimen, crushed longitudinally (fig. 13), shows that the species 
was rotund in section, as in P. punctatus and others. 
Antenne.—In all probability Plate XIII. [Plate 24] fig. 8, re- 
presents the antenna of this species. Its resemblance to those of 
P. problematicus is very close. The shaft is linear, the long end 
