1.104 NEW YORK STATE MUSEUM 



Fragments of Pterygotus 



Plate 24, fig. 6, 8 



In addition to the cephalothorax described above, other parts 

 were found, mainly mere fragments, having the coarse, scaly orna- 

 mentation of Pterygotus, but even the more perfect can not 

 be referred to definite' species, because of their isolated condi- 

 tion. Among these is an ovate metastoma [pi. 24, fig. 8] 

 27 mm long and 16 mm wide, broadest just anterior to the 

 middle, with the anterior corners slightly truncated, the lobes 

 small and the terminal notch very narrow and shallow. It is 

 marked by coarse, rounded, lobelike scales and is very much 

 more robust than would be expected in Pterygotus mon- 

 r o e n s i s . Judging by the ornamentation, it should be asso- 

 ciated with the coarse scaled fragments most frequently found. 



The broken, free ramus of a chela of a Pterygotus is repre 

 sented on plate 24, figure 6. The shaft is nearly parallel 

 sided, 3 mm broad and 12.5 mm long and curves at the end into 

 a stout, striated, nearly perpendicular mucro 3.5 mm long. 

 Back of this mucro is a series of 10 erect, sub triangular, striated 

 denticles, very slightly separated at their bases. They are of 

 three sizes, the largest or primaries being about one half the 

 length of the mucro, the secondaries one half that of the pri- 

 maries and the tertiaries about one half that of the secondaries. 

 The first primary is separated from the mucro by a secondary 

 and from the second primary by two secondaries and two ter- 

 tiaries alternating; following the second primary are two sec- 

 ondaries separated by a tertiary. 



The free ramus of Pt. buffaloensis Pohlman (14) 

 differs from this in having the shaft convex on the inner side; 

 the teeth perpendicular, numerous, acute, varied in length, one 

 or two longer ones about midway in the series; and the mucro 

 set at an acute angle. 



In P. cobbi Hall (10), the only other species of the Water- 

 lime in which this ramus is known, it is many times larger than 

 this fragment; shaft tapering; mucro less erect and blunt 

 tipped; teeth six, comparatively short, strong and unequal. 



Another fragment [pi. 24, fig. 1] represents the basal part 

 of the long, tapering, proximal joint of a chela of a Pterygotus. 



