EXPLANATION OF PLATE L L 



1 PTERINEA PLEUROPTERA (Conrad Sp.) Natural size, large specimen of left valve, from the 



Ludlow rock of Park Lane, Llandeilo. 



2 Small variety from the schists of CjTn y Brain. 



2 a Profile of both valves. 



2 h Part of surface magnified. 



3 PTERINEA SUBFALCATA (Conrad Sp.) Natural size, left valve, from the schists of Howgill 



FeU. 



3 a Magnified. 



J. PTERINEA TENUISTRIATA (M'Coy). Natural size, left valve, from the Upper Ludlow rock 

 of Benson Knot. 



4 a Magnified. 



5 PTERINEA ASPERULA (M"^Coy). From the shale of Builth Bridge, natm-al size, left valve. 



5 a Magnified. 



6 PTERINEA HIANS (M'^Coy). Natural size, left valve, from the Aymestry limestone, neai- Aymestry. 



6 a Magnified. 



7 PTERINEA RETROFLEXA (Wahl. Sp.) Variety (P. DEMISSA Conrad) left valve, natural 



size, from the Upper Ludlow quartzite of Kendal. 



7 a portion of surface at posterior slope magnified. 



8 Right valve of variety between var. a. and var. S. 



9, 10 Var. /3. NAVIFORMIS (Conrad). Natm-al size, from the Upper Ludlow rock, near Kendal. 



11 AVICULA DANBYI (M'^Coy). From the Upper Ludlow quartzite near Kendal, small quadrate 



specimen, of the radiated left, or convex, valve. 



12 Orbicular variety, natural size. 



13,14 Obliquely elongate varieties. 



15 Unradiated right or flat valve, natural size. 



16 MODIOLOPSIS INFLATA (M'Coy). From the schists of Pen Cerrig, left valve, natural size 



17 MODIOLOPSIS MODIOLARIS (Conrad Sp.) Right valve, of normal variety, from the schists of 



Cader Dinmael. 



18 Depressed variety, from the Caradoc sandstone of Horderly. 



19, 20 PTERINEA MEGALOBA (M-^Coy). Natural size, of small specimens, from the tilestone of 

 Storm Hill, Llandeilo. 



21 MODIOLOPSIS NILSONI (His. Sp.) Natural size, left valve, from the Ludlow rock. Park Lane, 



Llandeilo. 



22 MODIOLOPSIS POST-LINEATA (M'=Coy). Natural size, of right valve, from the schists of Alt 



yr Anker. 



23 ORTHONOTUS NASUTUS (Conrad). Natural size, right valve, from the Caradoc sandstone of 



Horderly. 



24 SANGUINOLITES DECIPIENS (M'^Coy). Natural size, right valve, from the Upper Ludlow, near 



Kendal. 



