176 SUPPLEMENT TO THE 



Genus — Orthis, Dalman. 1827. 

 82. Orthis Lapworthi, Bav. Sil Sup., PI. XIII, figs. 9, 10. 



Shell small, semicircular, wider than long, hinge-line straight, a little shorter than the 

 breadth of the shell ; dorsal valve moderately convex with a broad mesial sinus com- 

 mencing at the umbo, widening and deepening as it extends to the front, surface 

 ornamented with from ten to thirteen angular ribs ; ventral valve very convex, beak 

 nearly straight, very slightly incurved, area large, triangular, and bent backwards at right 

 angles to the plane of the valve, fissure open, surface ornamented with from eleven to 

 fourteen ribs, of which the central one is the largest and most prominent, and with a 

 shorter one on each side of it. The surface of the valves is closely marked with equi- 

 distant, concentric, projecting, scale-like laminge. 

 Length 2, breadth 3, depth \^ lines. 



Obs. — This little species was found by Mrs. R. Gray in the Llandeilo, or Balcletchie 

 Conglomerate, and in the Middle Caradoc at Shallock Mill, in Ayrshire. A similar shell 

 was also obtained by Mr. D. Brown from the Caradoc, in Peebleshire. 



I have named it after Prof. C. Lapworth, F.G.S., to whom we are indebted for an 

 excellent memoir on the ' Geology of the Girvan District of Ayrshire.' 



83. Orthis crispa, M'Coy. Dav., Sil. Mon., PI. XXXVIII, figs. 5—10; Sil. Sup., 



PI. XIII, figs. 7, 8. 



This species is fully described at p. 256 of my ' Silurian Monograph,' and my reason 

 for referring to it again is to say that the shell was found by Mrs. R. Gray in the 

 Llandeilo at Ardmillan Brae, and in the Upper Caradoc at Thraive, both in the Girvan 

 District of Ayrshire. It was also collected by the Geological Survey of Scotland in the 

 Caradoc or Wrae Limestone at Kilbucho, near the church, two and a quarter miles west 

 of Culter, in Peebleshire ; likewise in the same formation at Snar Water, Leadhills 

 District, Lanarkshire. A fragment of this shell was erroneously referred to Orthis 

 BoucJiardi in p. 15 of the Explanation of Sheet 15 of the Geological Map of Scotland. 



84. Orthis Balcletchiensis, Dav. Sil. Mon., PI. XXVI, fig. 23 ; Sil. Sup., PI. XIII, 



figs. 12—14. 



Shell transversely semi-circular or obscurely pentagonal, shghtly indented in front, 

 hinge-line straight, slightly less than the breadth of the shell; ventral valve very 



