REPORT OP THE STATE PALEONTOLOGIST 1902 1089 



jointed, chelate organs, so short that when extended they barely 

 equal one half the length of the cephalothoracic shield. The 

 pincers are edentulous and bevel-edged and in their normal posi- 

 tion lie folded over the basal joints so that their tips converge 

 close to the anterior border of the mouth. Extended, these 

 organs project beyond the border of the shield for perhaps half 

 their length; when turned straight back, their tips lap over 

 the end of the metastoma. In Pterygotus, on the contrary, 

 these organs are very long, having, at least in Pt. bilobus 

 Salter and Pt. macrophthalmus Hall, a length fully one 

 third that of the entire animal; and consist of ponderous, 

 dentate pincers supported on a slender, retrally tapering proxi- 

 mal joint of such a length as must necessarily have prevented 

 the pincers being used at the mouth, unless these appendages 

 were somewhat retractile, as suggested by Laurie (9). 



The next important difference is in the character of the spini- 

 form walking legs. As in Pterygotus, these consist of seven 

 joints, but the several pairs present a greater contrast in their 

 respective lengths, are proportionally more robust, and each 

 joint from the third to the sixth inclusive, carries a pair of ven- 

 trally and distally articulated, slender, curved spines. It is 

 doubtful if any species of Pterygotus has spines on these ap- 

 pendages; certainly, in several species in which these limbs 

 have been found apparently well preserved, they are lacking. 



Woodward (8) represents Pt. taurinus Salter as having 

 a spiniferous endognathite. Laurie, in his Anatomy and Rela- 

 tions of the Eurypteridae (9), in one place states that there is 

 no elaborate development of spines on the endognathites of 

 Pterygotus. Earlier in the same paper, however, he makes the 

 statement that they are destitute of anything in the way of 

 spines and, in a comparison of the appendages of Slimonia with 

 those of this genus, offers this explanation: "These [dentate, 

 preoral] appendages, unlike those of Slimonia, were probably 

 prehensile rather than masticatory, and this function may 

 account for the absence of spines on the other limbs (en- 

 dognathites), which are purely ambulatory." The converse of 

 this may be stated of Slimonia, and also of Hughmilleria, since 



