Chap. X.] 
UPPER SILURIAN CRUSTACEANS. 
239 
As tending to indicate an exact horizon for some of these species, it may be 
remarked that Pterygotus gigas, Salter, is now known to occur just at the junc- 
tion of the Silurian and Old Red formations at Kington ; whilst in beds a little 
higher, at Ludlow and at Kidderminster, the Pt. Ludensis, Salter, is the prevail- 
ing fossil. There is reason to believe that the beds in Forfarshire, in which 
the great Pterygotus Anglicus, its closest ally, is found, are of the same date. 
Both in Scotland and in Worcestershire Pterygotus is accompanied by 
Parka decipiens (see Chap. XI.), a fossil which Dr. J. Fleming supposed to 
be the fruit (or receptacle of the fruit) of some plant. There is strong reason 
for believing that these fossils are, on the contrary, the egg-packets of Ptery- 
gotus. They are of a discoid shape, and puckered and plaited from the 
point of attachment as from a centre. The appearance is as if a tough mem- 
brane containing rounded and rather soft egg-shaped bodies had suffered com- 
pression in the rock. The ovoid masses afford no indications of a style or 
stigma, such as must have been present had they been of the nature that Dr. 
Fleming supposed. That a great Crustacean, so like in many respects to the 
Copepoda, should have had large ovisacs, or that it deposited large masses of 
ova, on such aquatic vegetation as that noticed by Mr. Powrie in the same beds 
in Forfarshire, is far from unlikely, although the discoid shape of the fossil 
bodies * is different from that of the living forms. 
There are indications of several other species of Pterygotus in the Tilestones: 
Pt. Banksii, the least of them all, is here figured, Foss. 67. f. 2. 
Fossils (67). 
Pterygotus and Eurypterus, from the Tilestones of Kington. 
1. Eurypterus pyg- 2. Pterygotus Banksii, 
mseus, Salter. Salter. 
As far as has yet been ascertained, the genus Pterygotus preceded Eurypterus 
in time, the oldest Eurypterus yet found being E. cephalaspis Salter, from 
the Upper Ludlow rocks of Westmoreland ; but it seems to have continued 
longer in existence. E. pygmseus, Salter, Foss. 67. f. 1, a small and abundant 
species in the Tilestones at Kington and Ludlow, accompanies other species at 
the latter place. The genus occurs in beds of the same age in Russia, as already 
noted (p. 162). And, as we shall afterwards see, a fine species (or two) is 
blematicus, on the contrary, which commences * Dr. Mantell suggested that these were ova of 
in the Upper Ludlow rock, appears to range up Batrachians (Quart. Journ. Geol. Soc. vol. viii. 
into the Cornstones, having been found by Dr. p. 106 ; see also Lyell's Manual, oth edit., p. 421) ; 
John Harley, of King's College, in those beds and Mr. D. Page has remarked, that not only are 
at Hopton Grate, Ludlow, This is the highest some of them probably of vegetable origin, as de-* 
range of the genus known, and corresponds with scribed by Dr. Fleming, but others are possibly 
the great extent to which the supposed egg- the spawn of Batrachians and Mollusks, and even 
packets of this Crustacean (Parka decipiens) of the Crustaceans so common in the Old Ked 
are found in the Lower Old Eed Sandstone of (Advanced Textbook, 1856, p. 127). See also Geol. 
Forfarshire, — Tealing, near Dundee, and Car- Surv. Mem., Monograph I. p. 77. 
mylie, near Montrose, being localities rich in f Appendix to Pal. Foss. Woodw. Mus. pi. I E. 
Pterygoti. fig. 21. 
