EXPLANATION OF PLATE 3 F. 



1 PTERONITES PERSULCATQS (M^Coy). From the carboniferous limestone of Lowick, North- 



umberland ; right valve, natural size. 



2 LITHODOMUS JENKI NSONI (RrCoy). Left valve, natural size ; exhibiting faintly the large adductor 



impressions, and entire pallial scar ; from the carboniferous limestone of Lowick, Northumberland. 



2 a End view, shewing the anterior lunette, and inroUed beaks. 



3 SOLENIMYA PRIM.EVA (Phill.) Left valve, natural size ; internal cast, shewing the large muscular 



impressions, the faint anterior oblique ridge from the beak, and imperfectly the easts of the ridges behind 

 and before the posterior muscular impression; from the carboniferous limestone of Lowick, North- 

 umberland. 



3 a Back view, shewing the cartilage supports behind the beaks, as well as the faint divergent ridges in 



front of them. 



4 SANGUINOLITES SUBCARINATUS (M-'Coy). Right valve, natural size (the diagonal ridge not 



sharp enough), exhibiting portion of the inflected cartilage supports along the hinge-margin ; from the 

 carboniferous limestone of Lowick, Northumberland. 



5 SANGUINOLITES {Leptodomus) COSTELLATUS (M-^Coy). Left valve, natural size ; from carbo- 



niferous shales of Craige, near Kilmarnock. 



5 a Seen from the back, shewing the anterior and posterior lunettes or cartilage supports, and the small 



mesial sulcus of the posterior slope. 



6 SANGUINOLITES VARIABILIS (M^Coy). Right valve, natural size; from the limestone of 



Lowick, Northumberland. 



6 a Seen from behind, to shew the inflected dorsal margins. 



7 Ovate variety, without byssal sinus, and with very fine concentric plicse. 



7 a Small portion of surface of another specimen, highly magnified, shewing the lines of rough puncta 



crossing the concentric \vrinkles and membranous striae of the periostraca. 



8 Oblong variety. 



9 EDMONDIA RUDIS (M^Coy). Right valve, natural size; from the carboniferous Hmestone of 



Lowick, Northumberland. 

 10 EDMONDIA OBLONGA (M-^Coy). Right valve, natural size, internal cast, shewing the large 

 adductor impressions, connected by the simple pallial scar (the thick cartilage plate beneath the simple 

 cardinal margin too faintly expressed). 



10 a End view, to shew the anterior lunette (the indications of the thick cartilage plate on each side of 



the hinge-line too faint). 



11 SANGUINOLITES IRIDINOIDES (M'Coy). Right valve natural size, shewing a patch of the 



extremely thin shell near the middle of the dorsal margin, the remainder of the specimen being an 

 internal cast, shewing the thick cardinal ridge close under the hinge-line in the posterior portion, and the 

 large anterior adductor surmounted by its accessory impression at the anterior end ; from the limestone 

 of Lowick, Northumberland. 



11a Back view, to shew the wide, concave, inflected dorsal margins, and the sulcus left by one of the 



cardinal ridges, tapering to a point before reaching the beak, with two small patches of the very thin 

 shell adhering. 



12 SANGUINOLITES CLAVA (M<^Coy). Left valve, natural size, she\ving the impression of the 



anterior adductor at the anterior end ; from the carboniferous limestone near Llangollen, N. Wales. 



12 a Back view, to shew the wide anterior and posterior lunettes or inflected margins for the external 



cartilage. 



