140 BRITISH PALAEOZOIC PHYLLOCARIDA. 



moiety of the ridge or crest, and begins at 2 mm. behind the nuchal ridge; it 

 is 1^ mm. broad, and has a relatively high, sharp, tent-like section. Its left-hand 

 flange overlaps the dorsal edge of the valve for about \ mm. 



This condition of the dorsal crest evidently shows that it was superposed 

 on the two dorsal edges when they were in contact, overriding them like a ridge- 

 tile on a house-roof. 



From black shale, slightly calcareous, East Kilbride. 



In a specimen of two valves overlapping (right on left, one of them 63 X 

 25 mm.), also from E. Kilbride, in Mr. J. Neilson's Collection, a fragment of the 

 dorsal ridge, pushed off the junction of the valves, lies on the left valve, near its 

 dorsal margin. In this specimen of D. glabra, the striae of the postero- ventral 

 margin are relatively few in the portion preserved, being separate and strong. 



PI. XXIII, fig. 11. Mus. Sci. and Art Edin., \\ No. 5. 



Size. — Valves 43 mm. long, 17 mm. wide; abdominal segments 13 mm., not 

 easily separable in measurement, but probably antepenultimate 3 mm., pen- 

 ultimate 3 mm., ultimate 7 mm.; style and stylets about 12 mm. long. 



Characters. — Two valves displaced, seemingly right valves, but probably one 

 shows the inside of one valve and the other the outside of the other. The valve 

 nearest the top of the figure (and lying obliquely underneath the other) exhibits 

 a narrow, ribbon-like, flattened edge at the dorsal margin, looking like a flange of 

 the dorsal angular ridge, but probably due merely to local pressure. The dorsal 

 border of the overlying valve and the mesolateral ridge on each valve are not 

 quite so clearly defined as in the drawing. Both valves had a smooth surface, 

 which has been much wrinkled by pressure. The ventral margins in this specimen 

 bear rather narrow fringes, and this modified feature is observable in other 

 examples from Ardross. 



Hard dark-grey shale, slightly calcareous. Lower Carboniferous ; Ardross. 



2. Dithyrocaris ovalis, Woodivard and Etheridge, 1873. Mus. Geol. Surv. Scotl., 



F */, No. 4. Plate XVIII, figs. 3 a, b. 



Dithyrocaris ovalis, H. Woodicard and JR. Etheridge, junr., 1S73. Mein. 



Geol. Surv. Scotl., Explan. Sheet 23, 

 Appendix, p. 100. 

 — — Iidem, 1S74. Geol. Mag., dee. 2, vol. i, p. 107, pi. v, 



fig. 1; Eeport Brit. Assoc, for 1873 

 (1874), Sections, p. 92. 



