Vol. 52.] FAUNA OP THE KEISLEY LIMESTONE. 433 



Affinities. — The pygidium of L. margaritifer (Nieszk.) 1 very 

 closely resembles the one above described. The forked extremity, 

 the three rings on the axis, the course of the axal furrows with their 

 ends bending out to define the lanceolate areas on each side of the 

 post-axal area, the projection and shape of the two anterior pairs 

 of pleurge, and the general form of the pygidium are points of 

 similarity. The most conspicuous point of difference is the con- 

 tinuation of the axal furrows to the fork, which gives a very marked 

 appearance to this portion of the pygidium in the Keisley form, and 

 is in my opinion sufficient to separate it off as a distinct, though 

 allied, species. 



L. margaritifer occurs in the Borkholm Beds (F2) in East Russia, 

 and the occurrence of this English representative form L. bifurcatus 

 in the Keisley Limestone is another link between the faunas of the 

 two beds. 



Proetid^. 



CrpnASPis (Tornqtjistia, subgen. nov.) Nicholsoni, sp. n. (PL XXL 

 figs. 3 & 3 a.) 



There are four specimens of this new form in the Woodwardian 

 Museum Collection, 2 but in three cases the central portion only of 

 the head-shield is preserved, while in the fourth case the head- 

 shield has one free cheek attached, though slightly shifted out of 

 its natural position. 



The description of this species is as follows : — Head- shield nearly 

 semicircular, gently convex, 3 millim. long. Glabella broadly ovoid, 

 slightly and gradually narrowing towards the rounded anterior end. 

 Width at base nearly equal to length. Length equals about three- 

 fifths that of the head-shield. Glabella uniformly semicylindrical 

 in shape, rounded off in front. 



The base of the glabella occupies nearly one-third of the distance 

 between the points where facial sutures cut the hinder border of the 

 head-shield. The glabella possesses no basal lobes nor side-furrows. 



Axal furrows well marked, of constant depth and width, uniting 

 in front of the glabella, where at the median point of union a short 

 groove runs forward notching posteriorly the convex frontal area, 

 but not traversing it. At the antero-lateral angles of the glabella, 

 where the axal furrows curve inward round its front, there is on 

 each side a similar but longer groove running outward and slightly 

 forward over the swollen fixed cheek to the line of the facial suture, 

 and separating the frontal area from the fixed cheeks proper. This 

 triradiate group of grooves is a conspicuous feature of the head- 

 shield. 



Neck-furrow well marked, of the same width and depth as the 

 axal furrows. The neck-lobe measures from back to front, across 

 its middle, about a quarter the length of the glabella, but does not 

 rise to more than half the height of the latter. Behind the fixed 



1 Nieszkowski, ' Monogr. d. Trilob. d. Ostseeprov.' Archiv f. Naturk. Liv. 

 Est. u. Kurl. ser. 1, p. 568, pi. i. fig. 15. 



- There is another specimen (labelled Agnostus) in the Carlisle Museum. 



