Chap. X.] 
UPPER SILURIAN CRUSTACEANS. 
237 
Prof. M'Coy, from fish-defences, with which they were formerly confounded. 
(See p. 134.) That naturalist, indeed, supposed them to be the slender pincers 
of some large Crustacean, and hence called them Leptocheles, viz. L. (Ce- 
ratiocaris) leptodactylus (from the Lower Ludlow) and L. (C.) Murchisoni, 
PI. XIX. f. 1 ', but M. Barrande had, at the same time, found more perfect 
specimens in Bohemia, indicating that these long-pointed spines formed the trifid 
tail of a Crustacean, something like that of the Carboniferous genus Dithy- 
rocaris. His accurate figures, as yet unpublished, show, however, only the 
terminal segment of the abdomen. The perfect specimens from Ludlow and 
Lesmahago show the entire structure ; and we are now, therefore, able to 
unite all these forms in one genus. There cannot be less than twelve or fourteen 
species distributed in the Lower and Upper Ludlow rocks : some of them must 
have been nearly a foot in length, and others are minute *. 
The largest, if not the most highly organized, Crustacean in the Silurian list 
is the Pterygotus problematicus, Agas., before mentioned. The fragments of the 
body-rings, which are represented, PI. XIX. f. 4, 5, were at first considered by 
Agassiz to be fish-scales t ; but that author soon afterwards corrected his 
statement |, and assigned the animal its true place among the Crustacea. 
Reference has already been made to several other species, pp. 126, 140, the most 
gigantic of which, perhaps, occurs in the Tilestone quarries of Kington. The 
dimensions which Pt. problematicus (the Ludlow species) attained are un- 
known, — though, from fragments of the pincers described by Strickland and 
Salter §, it was probably not much smaller than the great Scotch Ptery- 
gotus, the ' Seraphim ' of the Scottish quarrymen, which must have been 5 
or 6 feet in length ||. Prof. M'Coy first referred Pterygotus to the Pcecilopoda 
(Limulus &c.) ; Mr. Henry Woodward has united the Eurypterida and Xiphosura 
in one order (Merostomata, of Dana) % of which the large King-crab (Limu- 
lus) is the modern type; and Professor James Hall has beautifully figured 
many complete specimens of Eurypterus from Buffalo, Lake Erie **. D'Eich- 
wald's and Professor Nieszkowski's ft figures of the Russian Eurypteri (see 
p. 162) are also very good ; and now that the entire form of Pterygotus itself 
has been discovered, they help to complete the evidence for the formation of 
a new suborder of Crustacea. These are the Eurypterida — already so named by 
Burmeister, but with a meaning different from that which the term now implies. 
In a memoir already quoted (Quart. Journ. Geol. Soc. vol. xii. p. 28), Pro- 
fessor Huxley has given reasons for considering these large Crustacea to be of 
a type nearly resembling some of the smallest of our living Decapod Crustacea 
(Alauna, Bodotria, Cuma, &c), and as even showing great similarity to the 
larval state of the higher forms ; and he adopts the term Eurypterida as in- 
cluding these two Palaeozoic genera (Pterygotus and Eurypterus), if not some 
others also, at present unsatisfactorily arranged among the Phyllopods|J. 
The entire form of Pterygotus was very simple (Foss. 26, p. 162) : — a small, 
half-oval, or subquadrate carapace, followed by thirteen convex body-rings, 
the last of which formed a pointed, truncate, or even bilobed tail-joint; two 
large, compound eyes on the sides of the carapace ; and beneath it the mouth 
is situated, protected by a large heart-shaped labrum. 
* See Geol. Mag. vol. iii. p. 203, pi. 10. figs. 8-10* ** Paleeont. New York, vol. iii. 1859, pp. 382, 
t Sil. Syst. p. 606. ' 419* and plates. 
I Poiss. Vieux Gres Kouge, pi. 1. ft Archiv Natur. Liv-, Esth- und Kurl. 1859 
§ Quart. Journ. G-eol. Soc. (1852) vol. viii. p. 1st ser. vol. ii. p. 299, pis. 1 & 2. 
386, pi. 21. H Seethe Memoir on these Palaeozoic Crustacea 
|| Pterygotus (Himantopterus) Banksii could by Huxley and Salter, Monograph I., Memoirs 
not have measured as many inches. Geological Survey of Great Britain, 1859. 
If Monograph, Paheont. Soc. 1866. 
