UPPER SILURIAN ROCKS OF THE PENTLAND HILLS. 



159 



This species seems sufficiently well characterised by the proportionate size, shape, and 

 position of the eyes. Among the British species it approaches E. Brewsteri (Woodward, 

 p. 151, pi. xviii. fig. 4) most nearly in the form of the carapace, but the eyes of 

 E. Brewsteri are proportionately very small. In fact I know of no species except 

 E. conicus, described above, in which the eyes are proportionately so large, and the 

 difference of position of the eyes and the shape of the body render the two forms quite 

 distinct. 



Drepanopterus, n. gen. 



Carapace broader than long ; widest about f ths from anterior margin. Body, 1st 

 segment wider than posterior margin of carapace ; increases in width to 3rd segment, and 

 then tapers rapidly. Limb elongated, sub cylindrical, terminating in a very slightly 

 expanded joint, concave on posterior margin. 



This genus I have ventured to create for the reception of a single form, viz. : — 



Drepanopterus pentlandicua (PI. III. figs. 16, 17.) 



The carapace is horseshoe-shaped, the breadth at the widest part, which is about f ths 

 of the length from the anterior margin, being 90 mm., and at the posterior margin only 

 77 mm. The length of the carapace is only about 46 mm., the proportion between it 

 and the breadth being about 4 to 7. The front margin is bent downwards, and there 

 does not seem to have been a distinct border. The surface of the carapace, which is 

 much crumpled, is covered with scale-markings, semicircular in form over the greater 

 part, but along the sides becoming more angular, with the convexity directed outwards. 

 The position of the eyes cannot be made out for certain, but they were probably placed 

 at about 15 mm. from the front of the carapace, and 12 mm. from the side. 



The body, of which portions of nine segments are preserved, is broad and conical in 

 form. The greatest breadth (96 mm.) is about the 3rd segment, and it narrows gradually 

 in the region of the 4th and 5th segments, and more abruptly in the succeeding ones. 



The length and breadth of the segments is as follows : — 



1st, 



8 mm. long. 



77 mm. wide. 



2nd, , 



. 13 „ 



94 



3rd, . 



. 10 ■ „ 



96 



4th, . 



10 „ . 



94 



5th, . 



9 „ 



82 



6th, . 



9 „ 



64 



7th, . 



. 10 „ 



44 



8th, . 



. 11 „ 



36 



9th, . 



....,, . , 



27 , 



The 1st segment is very small in proportion, and seems to taper towards the sides, so 

 that it does not appear along the margin. The 2nd and succeeding segments have their 

 outer and posterior margins curved, and overlap from before backwards. Near the centre 



VOL. XXXVII. PART I. (NO. 10). 2 B 



