EXPLANATION OF PLATE L K. 



1 ARCA {Byssoarca) SUBiEQUALIS (M'Coy). Natural size, seen along the hinge, to shew the 

 numerous equal teeth, from the sandstone of Lleehclawdd Myddfai. 



1 a Same specimen, side view. 



2 ARCA EDMONDIIFORMIS (M-'Coy). Natural size, right valve, from Alt yr Anker. 



3 Left valve. 



4 NUCULA LEVATA (Hall). Natural size, from Dinas Bran. 



.5 Less elongate variety. 



5 a Magnified to shew the hinge-teeth, and muscular impressions. 



6 NUCULITES POST-STRIATUS (Emmons). Natural size, from the schist of Gwyddelwern. 



7 CLIDOPHORUS OVALIS (M'Coy). Natural size, right valve, from sandy schists of Ceiriog 



WaterfaU. 



8 Left valve. 



9 CLIDOPHORUS PLANULATUS (Conrad Sp.) From Keeper's Lodge, Goldengrove. Natural 



size. 



10 ANONDONTOPSIS QUADRATUS (M^Coy). Natural size, from the tilestone of Storm Hill, 



Llandeilo. 



11 ANONDONTOPSIS BULLA (M^Coy). Left valve, natural size, from the Upper Ludlow rock of 



Kirkby Moor, Kendal. 

 ] 2 Right valve. 



1 3 Internal cast from Galway. 



14 ANONDONTOPSIS ANGUSTIFRONS (M<=Coy). Left valve, natural size, from the Upper Ludlow 



rock near Kendal. 



15 Right valve. 



16 AMBONYCHIA ? ACUTICOSTATA (M-'Coy). Natural size, from the schists of Dinas Bran. 



16 a Superficial ridges of ditto magnified. 



17 LYRODESMA PLANA (Conrad). Natural size, from the schists of Yspatty Evan. 



17 a Rostral portion of ditto magnified to shew the diverging teeth and cartilage pits. 



18 TELLINOMYA LINGULICOMES (M'^Coy). Natural size, two right and two left valves, from the 



slates of Penmorfa. 



19 SANGUINOLITES ANGULIFERUS (M-^Coy). Natural size of left valve, from the Upper 



Ludlow of Benson Knot. 



20 Right valve. 



21 LEPTODOMUS TRUNCATUS (M'=Coy). Natural size, of average form, right valve. Upper Ludlow 



of Benson Knot, Kendal. 



22 End view of both valves, shewing the anterior lunette. 



23 Remarkably elongate variety. 



24 Unusually short variety. 



25 ORTHONOTUS SEMISULCATUS (Sow. Sp.) Left valve, natural size, from the Upper Ludlow 



near Kendal. 



26 GRAMMYSIA ROTUNDATA (Sow. Sp.) Right valve, natural size, from the Upper Ludlow rock 



near Kendal. 



27 Left valve, to shew the two oblique furrows. 



