22, 23 0RTHIS TURGIDA (M'^Coy). Internal casts of entering valve, the former from Craig y Beri, and the 

 latter from hills North of Conway Falls. 



24 End view. 



25 ORTHIS SARMENTOSA (M"Coy). Natural size of transversely elongated specimen, from the schists of 



Llyn Ogwen. 



26 Internal cast of receiving valve of possibly normal form, shewing the high cardinal area and long dental 



lamellas. 



27 Internal cast of entering valve, shewing the slender rostral and dental teeth. 



28 Longitudinal section of both valves. 



29 ORTHISINA SCOTICA (RPCoy). Natural size, from the limestone of Craig Head, Ayrshire. 

 29 a Profile. 



29 h End view. 



30 LEPT^NA QUINQUECOSTATA (M'Coy). Natural size, transverse variety with additional lateral ridges, 



from the schists of Mathyrafal. 



31 Normal type from same locality. 



31 a Surface of ditto magnified. 



31 I Internal cast, shewing the short muscular impressions and the pallial ridges. 



32 Very large depressed variety from Colmonel on the Stinchar. 



33 LEPT^NA {Strophomena) SIMULANS (fll'^Coy). Convex or entering valve, natural size, from the schists 



of Cefn Coch ; with a portion of strise magnified. 



34 Concave or receiving valve, shewing the cast of the tubular foramen in the beak. 



34 a Longitudinal section. 



35 Internal cast of muscular impressions from Malvern. 



36 LEPT^NA {Leptagonia) UNGULA (M'Coy). Natural size, entering valve, from tlie limestone of 



Llansantfraid. 

 36 a Surface of ditto magnified. 



36 b Profile of ditto. 



37 Decorticated specimen of receiving valve, shewing the cast of the tubular foramen at tlie apex of tlie 



beak, the cardinal area and the cardinal teeth. 



37 a Profile of ditto. 



38 LEPT:ENA {Leptagonia) UNDATA (M'Coy). Natural size of a variety with continuous wrinkles, from 



Llwyn y Ci. 



39 Variety witli interrupted wrinkles, from Llandeilo. 



39 a Superficial stria? of ditto magnified. 



39 b Profile of both valves. 



39 c Internal cast of rostral portion of receiving valve, shewing the dental lamellfe, from Hryn Melyn, Bala. 



40 LEPTiENA TENUICINCTA (M''Coy). Natural size, from the schists of Cefn Grugos, shewing the entering 



valve, with the cardinal area and pseudodeltidium of receiving valve. 



40 a Profile of receiving valve. 



40 b Longitudinal section. 



40 c Striation of surface magnified. 



41 ORTHIS PORCATA (M'Coy). Natural size of receiving valve, from the limestone of Coniston. 

 41 a Striation of ditto magnified. 



41 b Rostral portion of internal cast of receiving valve, shewing the form of the muscular impressions. 



41 c Longitudinal section of both valves. 



42 Internal cast of entering valve, shewing the thick rostral and cardinal teeth, muscular impressions, and those 



of the pallial vessels. 



42 a Front view of entering valve. 



43 ORTHIS CRISPA (M'Coy). Natural size, from the Upper Bala rock of Bala. 

 43 a Profile of entering valve, and cardinal area of receiving valve. 



43 b Surface magnified. 



44 LEPT/ENA TENUISSIMESTRIATA (M'Coy). Natural size, from Llandeilo. 

 44 a Internal cast of ditto. 



446 Surface of ditto magnified, shewing the punctured sulci left by the removal of the shell in the upper portion. 



44 c Longitudinal section. 



