148 BRITISH PALEOZOIC PHYLLOCARIDA. 



hinder edge of the right valve (on the left-hand side of the figure) retains its 

 spine and part of the posterior notch. The hollow inside of a strong mesolateral 

 ridge is distinct in each valve. 



These insides show also the usual oblique lineation, due apparently to suc- 

 cessive overlapping of the flaky tissue of the test in its growth. The spaces 

 between the lines are pierced with close-set minute perforations (PI. XXIX, fig. 1), 

 individually blackened by the infilling of the black shale of the matrix. This 

 appearance is probably due to the removal, by decomposition, of both the outer 

 and inuer filmy coatings of the test. PI. XVIII, fig. 1 b, shows such a structure 

 in the test of Dlthyrocaris glabra, in which the removal of the delicately pitted 

 surface-layer exposes equivalent perforations in the next layer below. 



In hard grey calcareous shale. From the Lingula-Limestone at Jock's Burn, 

 below Hallcraig- Bridge, about one mile west of Carluke. Dr. Rankin Coll. 



PI. XIX, fig. 9. Mus. Pract. Geol., No. 6368. 



Size. — Length of valve about 34 mm. ; breadth of valve about 18 mm. 



Characters. — Two valves, lying one on another ; the dorsal edge of the left 

 (uppermost) valve shifted on and beyond that of the other valve. The ventral 

 border of the right valve (undermost) shows the serrated edge, or fringe, 

 thinning away forwards. Bounded inside by a thin definite parallel ridge, this 

 corresponds to the " double margin " of other species. Each valve has a mesial 

 ridge, somewhat rugose here and there. Postero-ventral spines are well shown. 

 The surface obliquely striated as usual. 



A little obliquely sub-oblong Posidonomya, looking almost silky with its 

 numerous delicate, concentric stria3, lies on the same piece of hard, grey-black, 

 micaceous shale, non-calcareous, from the Glasgow Coal-field. 



PL XXI, fig. 1. Brit. Mus. No. 59451, No. 17. 



Size. — Length of valve 50 mm. ; breadth of valve 20 mm. 



Characters. — A large left valve, perfect in outline, but filmy in substance; 

 dorsally apposed to an imperfect right valve ; the junction indicated by the position 

 of the front and hinder notches. The mesolateral ridge is rugose in its posterior 

 portion ; the ventral border retains some of its fringed outer margin, and its 

 posterior spine. 



In black shale, very slightly calcareous. From East Kilbride. 



PI. XXI, fig. 2. Brit. Mus. No. 46395, No. 18. 

 Size. — Length of valve 45 mm. ; breadth of valve about 18 mm. 

 Characters. — Two imperfect valves, closely adpressed and obscurely overlap- 

 ping on the dorsal border. The ventral border of the left valve has left no mark 



