On the Crustacean genus Stylonurus. 231 



terido?, 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 

 members — the three first variously formed in the different 

 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. 

 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 Eurypteridce 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 

 Stylonurus discovered was S. Powriei, 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 Ptcrygotus, 

 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 Ked Sandstone of 

 Forfarshire, and specimens indicated its dimensions as vary- 

 ing from eight to eighteen inches in length. The next 

 species, S. S2)inipcs, had been discovered in the " Passage- 



