﻿PTERYGOTUS BILOBUS. 



GO 



Ion' 



broad. 





a ' 



- j 



c \ 





Head 



(1-7) 



15 lines by 2 



inches 





Body-segment 



(8) 



4 



, 2 



) > 





)> 





(9) 



6 



, 2 



>> 



2 lines. 



» 





(10) 



7 



, 2 



y> 



4 „ 



)> 





CO 



6 



9 



!> 



6 „ 



» 





(12) 



5 



„ 2 



)» 



6 „ 



5J 





(13) 



5 



„ 2 



>i 



5 » 



»> 





(14) 



4 



.. 2 



)) 



2 „ 



!! 





(15) 



6? 



, 1 



)> 



9 „ ? 



)! 





(16) 



6? 



, 1 



?5 



7 „ ? 



)) 





(17) 



G 



„ 1 



)? 



4 „ 



>> 





(18) 



6 



, 1 



>> 



4 „ 



?? 





(19) 



9 



„ 1 



)J 





Telson 





(20) 



15 



, 1 



>1 



1 line. 



The surface of the head is not ornamented in any way, but the bases of the jaw-feet, 

 the thoracic plate (see Woodcut, fig. 13), and the anterior third of the body-segments, 

 are closely covered with minute plicae. 



The portion of magnified scale-markings drawn by Mr. Hollick in PI. XII, fig. 

 1 c, are from the body-segment (io) ; the squamae are so close together that they actually 

 present the appearance represented, but there is no real overlapping of scales, only a 

 mimetic resemblance to it. Along the anterior border the scale-markings are very fine, 

 closely packed, and but little arched ; lower down they become more acute and consider- 

 ably larger ; whilst on the lateral borders they are extremely minute and packed very close 

 together. The edges of all the segments are very minutely serrated, as in the larger 

 Devonian species. The thoracic plate, which is very well preserved, is about 2 inches 

 in breadth by about 10 lines in length. 



Fig. 13. Thoracic plate or operculum of Pt. bitobus, var. S. 1 

 a, a. Line of attachment to posterior border of head-shield. /./. Free border, c. Central appendage. 



1 The representation of the operculum in Pi. XII, fig. 1 e, is not quite correct. This Woodcut conveys 

 a better idea of its form. 



10 



