250 DESCRIPTION OF THE SPECIES OF PTERYGOTUS 
The large chela, figured as above under this name, by the late 
Mr. Strickland and myself, proves to be really an appendage of this 
same species, at least it is always associated with it in the same bed. 
Again, the antennary portions, fragments of body rings, bases of the 
swimming feet, post-oral plate, &c., figured on Plate XII. [Plate 23], 
are all found in the Whitcliffe, Ludlow, or other localities of the 
Upper Ludlow Rock, and clearly differ from the corresponding parts 
in P. punctatus, the only other large species occurring with them, 
as well as from those just described, which are characteristic of the 
beds of passage above the top of the Ludlow series. P. problematicis 
may now, therefore, be considered an established species, and the 
cabinets of our Ludlow friends, Messrs. Cocking and Marston, have 
furnished many of the materials. It occurs, too, in plenty, as Mr. 
Lightbody’s researches show, in the transition beds beneath the Old 
Red Sandstone, Plate XIV. [Plate 25]; and Mr. J. Harley, to 
whom we are indebted for much valuable help, has been fortunate 
enough to detect its fragments far up in the cornstones of the Old 
Red itself, a higher limit than the genus had been known before to. 
attain, 
[If the large fragments from the transition beds above quoted, 
and figured on Plate XIV. [Plate 25], be of the same species, as 
the sculpture indicates, the body segments attained a very large size, 
nearly three inches from back to front. As it is possible these may 
belong to a different species, I will describe these portions first. 
Carapace (?), Plate NIV. [Plate 25] fig. 16—A fragment, three 
inches by two and a half, has the surface sculptured, unlike the 
body rings, ze, much more finely marked, and without the regular 
increase in size and curve of the plice backwards. The anterior 
ones are nearly as much bent as the hinder ones though smaller— 
all are but slightly prominent, and are covered by numerous smaller 
plice. 
Body Rings, Plate XIV. [Plate 25] fig. 17.—One of the broad 
abdominal rings, two inches and three-quarters from back to front: 
the articulating front margin is rather deeply concave, and its edge 
is obscurely striate longitudinally (like fig. 3). The plice are 
very numerous and close-set, not so large as in P. anglicus, or so 
straight on the forward edge, where, however, they are very closely 
packed. They are more open posteriorly, and cover more than half 
the segment, interspersed with very numerous minute semicircular 
plaits. 
Another piece (fig. 14) is here considered as belonging to this 
species, but it only shows the interspersed plicee over part of the 
