On the Crustacean genus Styloniirns. 231 
teridm, the members of which were distinguished {in the 
dorsal aspect) by their rounded or sub-quadrate carapaces 
or head-plates, with central, sub-central, or marginal eyes ; 
by their lobster-like thoracico-abdominal segments, twelve 
in number, and void of appendages ; and by their single- 
pieced telsons or tail-plates, which were oval and pointed, 
heart-shaped, or long and style-shaped, as in the genus 
now under review. The carapaces {in the oral or ventral 
aspect) were furnished with four pairs of five or six jointed 
j members — the three first variously formed in the different 
I genera (some armed with spines, others with prehensile 
pincers), and the posterior pair forming the broad, oar-like 
swimming feet, which had given the name to the family, 
j. The oral apparatus consisted, as in the King-crab, of the 
serrated basal joints of the limbs, and was protected by a 
broad heart-shaped metastome or mouthpiece. The geni- 
tal and anal orifice occurred in the first thoracic segment, 
and differed, both in situation and appendages, from all 
known Crustacea. In all the genera the exterior crust was 
ornamented by a peculiar scale-like sculpture, which became 
bolder and stronger on the free or exposed margins of the 
respective segments, and in several of the species passed 
into a peculiar serrated or bead-like ornamentation. 
The Eurypteridm ranged in time from the Upper Silurian 
to the Carboniferous limestone inclusive, and some of them 
were of gigantic dimensions — the Forfarshire Pterygoti and 
Stylonuri often ranging from four to six feet in length, 
and in other parts of corresponding dimensions. The first 
Siylonurus discovered was S, Fowriei, distinguished by its 
very rounded carapace, central eyes, long, pointed, and per- 
haps caniculated tail-plate, and by its swimming limbs, 
which, instead of being paddle-shaped as in Fterygotus, 
were long, narrow, and ensiform. This species had two 
pairs of similar swimming limbs; the anterior limbs had 
not been preserved, and were accordingly unknown. It had 
yet been found chiefly in the lower Old Eed Sandstone of 
Forfarshire, and specimens indicated its dimensions as vary- 
ing from eight to eighteen inches in length. The next 
species, S. spinipes^ had been discovered in the Passage- 
