1865.] n. >Y00DWAIID— 'DEVONIAN CRUSTACEA. 483 



up the sides, which rapidly contract for one-fourth of their length 

 before reaching the posterior angle. 



The eyes are placed |ths of an inch apart on either side of a me- 

 dian furrow, which, passing forward, divides into two semicircular 

 arches, and is lost in a series of minute tuberculations. On either side 

 of the median line are two small oblong tubercles, placed between and 

 slightly in front of the eyes. The eyes themselves can hardly be 

 said to be preserved in this specimen, but their position is clearly 

 indicated. 



Only two pairs of long appendages in S. Potvriei are known. The 

 basal joints of these were furnished with palpi, as in Pterygotus, Eu- 

 rypteriis, and Slimonia. They appear to have been eight-jointed, 

 the first joints being broad and flat, and no doubt precisely like that 

 of Stylonurus Logani, mihi* ; the second, a short articulation not 

 clearly seen ; the third, about one 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 3 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, |ths of an inch long; 

 fifth, 2 inches 3 lines broad, 5 lines long ; sixth, 2 inches broad, 5 

 lines long; seventh (or first abdominal), 5 lines (about) long, 

 1 inch 7 Knes 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 hues broad ; 

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

 semicircular curve into which the anterior margin of the tail is in- 

 serted. 



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 Jg-th of an inch in -nddth. Two zigzag lines of plica) 

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

 about |ths 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 Avhich the mus- 

 cular attachment within was strongest. 



The thoracic segments are slightly spinose along their posterior 

 margins. S. Powriei had, probably, epimeral pieces to its abdominal 

 segments : but, being as before stated a cast, these pieces would not 

 * See ' G-eological Magazine,' vol. i. p. 197, pi- 10. fig. 1. 



