216 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
“This small neat species, of which we have many specimens in 
the Museum of Practical Geology, occurs with Pterygotus (P. gigas, 
Plate VIII. [Plate 19]), and spines both of Crustacea and fish, in 
the yellow tilestone (Downton Sandstone) beds of Kington, Hereford- 
shire. It is there associated with the Platyschisma helicites and 
Lingula cornea, Sil. Syst. These are the two species of shells which 
accompany the fossils of Lesmahago above described, a good argu- 
ment, therefore, even without other evidence, for regarding these 
Lesmahago beds as the uppermost portions of the Ludlow rock.’— 
Quart. Geol. Journ. 0. c. 
Description —The full size must have been from four to five 
inches long, but the specimens usually met with would probably not 
be above three or four inches. One or two show the connexion of 
the body rings with the head and appendages, fig. 42, or with the tail 
joint (fig. 23). None are quite complete, and though we have nearly 
all the parts, they are usually disjointed. 
The carapace (fig. 22) is a broad semioval, its length as six to 
seven, except when lengthened or shortened by pressure (figs. 25, 26). 
It is regularly convex, a little angulated in front, smooth, and bears 
the small oval eyes rather more than half-way up the head. They 
are much smaller than in //. éz/obus, being not above one-fourth the 
length of the carapace, and very convex. 
The body is at first wider than the head and then tapers back- 
wards, The first ring is very narrow (fig. 42), the second twice as 
broad and with the usual dilated extremities ; the third, fourth, and 
fifth strap-shaped, arched in the middle and direct on the sides, so 
that the segment appears much bent. The ends are truncate, in 
the anterior rings widest behind, and in the posterior ones tapering 
backwards. 
Fig. 28 shows one of the hindermost rings, such as are seen in 
the more complete specimen, fig. 23. The hinder rings become 
gradually less transverse, the tenth only two and a half times wider 
than long, and the penultimate about once and three-quarters its 
own length. 
The caudal joint (telson) figs. 23, 38, 45, differs, in its expanded 
form, materially from that of A. dzlobus. It is about three-fourths 
as long as wide, narrow at the base with two short ridges running 
down from either angle ; then expanded with somewhat convex sides 
towards the wide subtruncate apex ; the outer angles are rounded off, 
the terminal notch shallow, and a short median keel continued from 
it one-third up the segment. 
The sculpture of the head is not known. On the body rings a 
