244 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
PLATES VIII. anp IX. [PLATES 19, 20]. 
PTERYGOTUS GIGAS. 
Spec. CHAR. P. maximus, 6-7 pedalis (?), capite haud truncato, semiovato ; 
oculis anticis rotundis , segments corporis ut in P. anglico,--penultimo expanso 
emarginato, insuper plano, subtis caring mediand postica : caud&é magna oval, 
crista elevata central (apice emarginato ?). 
SynonyM. PP. problematicus, BANKS, Quart. Journ. Geol. Soc. vol. xii. 
pp- 93, &c. 
For some years a large Prerygotus has been known in the beds of 
Downton Sandstone (Uppermost Ludlow Rock), worked for building 
purposes at Kington, Herefordshire, and a description of many of its 
parts was given by Mr. R. Banks, of Ridgbourne, in the Quarterly 
Journal of the Geological Society for 1856. Since his description 
was written, he has continued to labour assiduously to collect the 
fragments, and has been fortunate enough to discover nearly all the 
parts of this fine species. He has generously placed these fragile 
specimens in our hands, and presented a series of excellent drawings, 
which were formerly exhibited at the Geological Society.) In the 
paper quoted above, the fragments were all considered to belong 
to the P problematicus of Agassiz, a species for which there is un- 
fortunately very scanty material, but which, as originally described 
(see below, Plate NII. [Plate 23]) is a Ludlow Rock species identical 
with one of the Kington fossils, but not apparently with the principal 
and largest of them, here described, and which in many respects is. 
very like P. anglrcus. 
P. gigas has, in common with the latter species, the open scale- 
like sculpture on the body rings, and the thick tubercular scales on 
their margin; the shape of the epistome and head is very similar, 
but the latter is rounded and not truncate in front. The penultimate 
body ring is wider and has a short keel on the upper surface only 
(while P. axglicus has one on both sides above and below), and 
the tail joint or telson appears to be emarginate instead of pointed. 
But if this character should be deceptive, there can be no doubt of 
the specific difference, since this joint is furnished with a most re- 
markable elevated crest or ridge nearly half an inch high, which is 
quite absent in the Scotch species. 
1 See Quart. Journ. as above, note to p- 97. It ought to have been named after him, 
had not a much smaller Kington species been already distinguished by his name. 
