170 SUPPLEMENT TO THE 



from the Upper Llandovery at Penkill, the Middle Llandovery, at Woodlands Point, the 

 Middle Caradoc, at Whitehouse Bay and Shallock Mill, in the Upper Llandeilo, at Ard- 

 millan Brae and Batcletchie in Ayrshire. It varies much in the number of its principal 

 thread-like radii, some specimens show only three, others four, five, and six. Whether it 

 is more than a variety of Leptana sericea has still to be determined. 



71. Lept^ena Etheridgei, Dav. Sup., PI. XII, figs. 11, 12. 



Shell marginally semicircular, tapering shghtly anteriorly; hinge-line long, straight, 

 slightly less than the breadth of the shell. Ventral valve evenly convex, area narrow ; 

 beak small and slightly incurved ; dorsal valve concave, following the curves of the 

 opposite one ; hinge-area narrow, fissure small. Surface marked by very fine radiating 

 lines and a few indistinct thread-like radii. 

 Length 5, width 6 lines. 



In the interior of the dorsal valve the muscular area occupies half the length and 

 one third of the breadth of the valve, these scars form two wide, elongated, oval-shaped 

 impressions, much raised anteriorly, especially from the bottom of the valve ; these 

 impressions are separated by an intervening concave space, along the centre of which 

 there is a narrow median septum. The cardinal process is small, and there is a wide 

 convex ridge all round the interior margin of the valve. The interior of the ventral valve 

 is not known. 



Obs. — This small species is much more circular and less transverse than L. sericea, 

 and seems to differ from it by the shape of its muscular impressions. Several specimens 

 were found by Mrs. R. Gray in the Upper Llandeilo at Craighead, in Ayrshire. I have 

 named it after Mr. R. Etheridge, E.R.S., to whose labours science is much indebted. 



72. Lept^na scissa. Salt. Dav., Sil. Hon., PI. XL VII, figs. 21—25 ; Sil. Sup., PI. 



XII, fig. 22. 



Two very finely preserved internal casts of this well-marked species were found by 

 Mr. R. Philip in grit at the top of the Upper Llandovery at Minsterley, in Shropshire, and 

 forming part of that formation. 



