STYLONURUS POWRIEI. 123 



these were, no doubt, furnished with palpi, as in Pterygotus, Eurypterus, and Slimonia. 

 They appear to have been eight-jointed, the first joints being broad and flat, precisely 

 like that of Stylonurus Logani ; the second, a short articulation not clearly seen; 

 the third, about 1 inch in length, and having a keel down the centre ; the fourth, 

 10 lines in length, also keeled; the fifth and sixth, 7 lines; the seventh and eighth, 



6 lines each. The third and fourth joints seem to have been about 5 lines in width, and 

 the others slightly narrower to the eighth, which terminates in a fine slender point, 

 slightly incurved. The two pairs of limbs on either side appear to have been about 

 equal both in length and breadth. 



The Body -segments, twelve in number, increase gradually in breadth to the fourth, 

 when they as gradually decrease to the eighth, whilst the four remaining segments rapidly 

 decrease in breadth and increase in length. 



Dimensions. — Thoracic segments : — First, 2 inches three lines broad, 3 lines long ; 

 second, 2 inches 5 lines broad, 5 lines long ; third, 2 inches 5 lines broad, 5 lines long ; 

 fourth, 2-| inches broad, f ths of an inch long ; fifth, 2 inches 3 lines broad, 5 lines long ; 

 sixth, 2 inches 5 lines long ; seventh (or first abdominal), 5 lines (about) long, 1 inch 



7 lines broad (about); eighth (or second abdominal), 5 lines long, 1^ inch broad; 

 ninth (or third abdominal), 9 lines long, 17 lines broad ; tenth (or fourth abdominal), 

 5 lines long, 14 lines broad; eleventh (or fifth abdominal), 6 lines long, 10 lines broad; 

 twelfth (or sixth abdominal), 5 lines long, 9 lines broad, forming a semicircular curve 

 into which the proximal end of the tail is inserted. 



The Telson, or tail-spine, is 3 inches 10 lines in length, nearly 3 lines broad through 

 its entire length, having a deep groove down its centre Ygth of an inch in width. Two 

 zigzag lines of plicae pass down from the head, on either side of the thoracic segments, 

 about fths of an inch from their lateral margins. These markings appear to be due to 

 compression, and, as they are also noticeable in the Lanarkshire specimen, are probably 

 lines along which muscular attachment within was strongest. 



The Thoracic segments are slightly spinose along their posterior margins. S. Poioriei 

 had, probably, epimeral pieces to its abdominal segments ; but being, as before stated, a 

 cast, these pieces would not be shown attached, but remain upon the exterior slab, as is 

 the case both in Pterygotus Anglicus in the Arbroath Museum, and Stylonurus Scotictis 

 described herewith. 



On PL XXI, fig. 2, is represented two detached parts of the long swimming appen- 

 dages of Stylonurus, which, from their size, belonged to an individual larger than 

 S. Poioriei (fig. 1). The specimen shows that the joints were strongly keeled down the 

 centre, and slightly serrated along the inner border. 



Formation. — PI. XXI, fig. 1, Old Red Sandstone; fig. 2, Upper Silurian. 



Locality. — Fig. 1, Turin Hill range, Pitscandly, Forfarshire; fig. 2, Lesmahagow, 

 Lanarkshire. 



From the collection of James Powrie, Esq., F.G.S., Reswallie. 



