DESCRIPTION OF THE SPECIES OF PTERYGOTUS 249 
like that of P. anglicus, Plate VI. [Plate 17], and chiefly differs in 
the more contracted base, and large open plicz of the surface. The 
notch is somewhat deeper. It may have been smooth over the 
hinder portion, as in Plate XII. [Plate 23] fig. 3, which is the 
same or a closely allied species, and may be noticed here, though 
possibly it belongs to P. dudensis, above described. 
Plate XII. [Plate 23] fig. 3—-This post-oral plate, in its an- 
terior portion, a good deal resembles that figured in Plate IN. 
[Plate 20], the notch being a little less deep only. The shape 
is much more elongate than in P. anglicus, the length being as seven 
to four; the width is greatest at the anterior third, and the general 
shape ovate. The plice are large and open, and are confined to the 
anterior portion about the notch. 
The basal joint of the swimming foot (fig. 6), found at the same 
locality, is in almost every respect like that of P. gégas, having the 
teeth broad and short. 
Locality —Downton Sandstone (UPPERMOS? LUDLOW ROCK) of 
Kington, Herefordshire. (Cabinet of Mr. R. Banks, of that place.) 
Some specimens, presented by that gentleman, are in the Museum 
of Practical Geology. Plate XII. [Plate 23] figs. 3, 6, are also 
specimens in the Museum, collected by Mr. A. Marston, of Ludlow. 
They were found at the Ludlow Railway Bridge, in the passage beds 
at the base of the Old Red Sandstone. 
PLATE XII. [PLATE 23] Fics. 7-16, 20, 213 AND PLaTe NIV. [PLATE 25] 
Fics. 16-18. 
P. PROBLEMATICUS. 
P. magnus, segmentis corporis ornatissimis,—plicts minutis creberrimis inter 
majores mixtis (segmento ultimo transverse, Nec expanse, subtis carind brevt 
mediand ?) - antennis dentibus longis, rectis, remotts. 
Synonym. P. prodblematicus, AGASS., in Sil. Syst. (1839), p. 606, pl. 4, 
figs. 4, 5 (? Sphagodus pristodontus, AG., tooth only, ib. fig. 6). STRICKLAND 
and SALTER, Quart. Journ. Geol. Soc., vol. vill, pl. 21, figs. 1, 2; Siluria, 
and ed. pl. 19, figs. 4-6. 
As this is the principal, if not the only species in the true Upper 
Ludlow Rock, which has the usual semicircular ornamental plice, it 
is to this that the name prodlematicus should be given, and, fortunately, 
on one of the minute original fragments figured in the “Silurian 
System,” the small intermediate plicae are to be seen marking the 
species more definitely. 
