CYBELE BELLATULA. 41 



posterior part of the thorax and pygidium extremely Avell; the spinose ends of 

 the seventh and followmg pairs of pleurae are seen to be produced back to about the 

 same level, i. e. to about the end of the pygidium. The stouter and longer spinose 

 ends of the sixth pair of pleurce reach back to a point behind the pygidium equal 

 to at least the length of the latter. This species, and apparently the same variety 

 of it, has also now to be recorded from the Whitehouse Group, for Mrs. Gray has 

 found at Whitehouse Bay a well-marked head-shield, and also a small pygidium 

 about 7 mm. lono^. 



Cybele bellatula, Dalman, var. nov. balclatchiensis. Plate VII, fig. 6. 



In a fairly well-preserved thorax and pygidium of a species of Cyhele from 



Balclatchie, the sixth (or seventh) thoracic segment has its pleurge much stouter, 



broader and longer than the preceding ones, and they are produced back as long 



curved spines as far as or further than the tip of the pygidium, as in G. loveni var. 



glrvanensis. The pleurae of the segments behind the sixth one are likewise 



elongated into spines which decrease successively in length. Brogger^ has shown 



this feature to exist in G. loveni. In the American G. wincheUi'^ it is only the 



sixth pleura which is elongated and enlarged. The other thoracic pleurge of our 



Balclatchie form have the characters described in the specimens which have been 



referred by me^ to C. bellatula, Dalman, a strong rounded median ridge having a 



narrow depressed band on each edge. The pygidium attached to the thorax 



possessing these spinose posterior pleurse is triangular in shape, and has a narrow 



elongated conical axis about three-fourths the length of the pygidium, with a narrow 



ridged and pointed conical post-axial piece extending from its tip to the margin. 



The axis is annulated to its blunt extremity by 1 7 — 18 narrow incomplete rings, with 



the median third smooth, and a pair of small tubercles is situated on each ring 



where it abuts against this smooth zone. The lateral lobes are composed of four 



pairs of pleurge, the two posterior ones rendered indistinct by a curious subreticulate 



ornamentation (? pathological) of circular, elongated or irregularly fused pits 



covering the surface. The pleurae are duplicate, being composed of two unequally 



developed ridges, the posterior one being the stronger ; all end in free slightly 



recurved points on the margin, successively reaching further back along the sides 



of the pygidium. The first pair of pleuras is the largest and most clearly divided 



into anterior and posterior ridges, the latter ridge being the stronger one, and 



embraces nearly three-fourths of the whole side of the pygidium, the free point 



being at about the level of the end of the axis. The third and fourth pairs of 



pleurae have their ridges very slender and weak, and are difficult to distinguish 



1 Brogger, ' Die Silur. Etagen, 2 and 3,' p. 136, pi. vi, fig. 2. 



2 Clarke, ' Palseont. Minnesota,' vol. iii (1894), p. 742, text-iig. 59. 

 ■' Reed, 'Giivan Trilobites,' pt. iii, p. 124, pi. xvi, fig. 15. 



