506 :ur. w. 13. h. Ki'SG ox the [vol. lxxix, 



notch of the posterior margin. Three well-developed axial rings 

 are preserved on the anterior part of the axis. The lateral parts 

 of the pygidium consist of three pairs of pleurae similar to those of 

 L. geilcei ; but the first two have the median pleural furrow even 

 more strongly developed. All pleurae extend to beyond the 

 margin, leaving marked notches in the border. Surface ornamented 

 by tine granules. 



Dimensions. — Width of pygidium = 3 '5 mm.; length = 

 2 '6 mm. 



Phacops (Pterygometoptts) broxgkiartt Portlock. var. 

 (PL XXVI, figs. 4 & 5.) 



An almost complete enrolled specimen was obtained from the 

 higher part of the Calymene-quaclrata Beds on Craig-fawr 

 (c'S locality, fig. 3, p. 496). 



The head- shield is very similar to that of JPt. trongniarti Port- 

 lock, the only differences being variations in intensity of character 

 rather than in shape : thus, the neck-furrow and groove on the 

 fixed cheek at its junction with the eye seem to be less developed 

 in this specimen, while the anterior (cat's ear) glabellar lobe is 

 rather more pointed anteriorly. The pygidium shows, however, 

 considerable differences ; the variety is distinctly pointed, while 

 the pleurae, although clearly but not deeply marked off one from 

 the other, show no signs of the bifurcation which Portlock notes 

 as one of the characteristics of his species. 



Dimensions in millimetres. 



Glabella ; length 10 



Glabella ; width (genal angle) 17 



Pygidium ; length 10 



Pygidium ; width 14 



As only one specimen of this form has been found, it is probably 

 advisable to consider it as a variety of Portlock's species, until 

 other specimens have been obtained and we can see whether the 

 characters noted above are constant. 



Christia>"ta testuicincta (M'Coy). 



This is one of the most characteristic fossils of the Ashgillian of 

 the area. The forms in the lower PMllipsinella Beds are small 

 (7 to 8 mm.) and generally of the same length as width ; but, in 

 the higher beds (Calymene-quaclrata Beds), they attain much 

 larger dimensions, and tend to group into two types : (a) elongate 

 form and (b) rotund form. 



Individuals gave the following measurements in millimetres: — 



(a) Length = 19; width = 14. 



(b) Length = 13; width = 15. 



This species appears to be almost restricted to the Ashgillian, 

 and it should he noted that the specimen figured by Thomas 



