REPORT OF THE STATE PALEONTOLOGIST 1902 1105 



These fragments show the genus Pterygotus to be fairly well 

 represented in the black shale by species, though not by num- 

 bers. 



Genus (?) 



Plate 26, fig. 1, 2, 4 



An eurypterid differing very materially from anything de- 

 scribed from the Bertie waterlime, is represented in the collec- 

 tion by a group of four incomplete arms and a body segment, 

 and by another of two incomplete arms. 



In the first group [pi. 26, fig. 2] the longest of the arms 

 has the coxal and succeeding five joints preserved. These are 

 long, measuring altogether 110 mm in length. The three distal 

 bear a series of long, curved spines. The form of the coxal 

 joint is subtrapezoidal, the anterior side being considerably the 

 longer. The breadth and the mean length are each about 18 

 mm. The dentate border is slightly produced and in length 

 is equal to about one half the breadth of the joint. The denta- 

 tion begins at the front end with an isolated, blunt tooth point- 

 ing forward, followed by sharp, curved teeth of small size which 

 grade posteriorly into fine, hairlike bristles. The anterior side 

 of each joint from the second to the sixth inclusive, is arcuate. 

 The posterior sides of the second and third joints are straight, 

 of the fourth, fifth and sixth, concave. The distal end of each 

 is at right angles to the long axis. The second joint is nar- 

 rower (14.5 mm) than long (23 mm); the third just twice as long 

 (28 mm) as wide (14 mm); the fourth a little longer than the 

 preceding (30 mm) and less than half as wide (7 mm). Along 

 the concave, posterior side of the fourth are articulated five, 

 long, curved, striated spines, nearly perpendicular to the joint. 

 At the distal end of the series there is an indication of another. 

 The most complete of these spines is 16 mm in length. The 

 fifth joint is 16 mm long and 6 mm wide. Near the anterior 

 end of the posterior edge it carries the stump of a large spine fol- 

 lowed by the sockets of four more. The sixth joint bears the 

 basal portion of three spines, but is so crushed and fore- 

 shortened that neither the original number of spines nor the 

 length of the joint can be determined. Judging by the taper of 

 this arm, there may have been two more joints. 



