EDMONDIA SENILIS. 151 



I have no doubt that the shells referred to Carbonicola robusta and Myalina 

 triangularis were Edmondia amsena and Myalina Vernewillii. The former two 

 species do not occur with purely marine forms. 



Edmondia acuta, sp. nov. Plate XXIV, figs. 3 — 5. 



Specific Characters. — Shell of medium size, transversely ovate, inequilateral, 

 broad in front, narrow posteriorly, tumid. The anterior end well developed, its 

 border rounded. Inferior margin convex, posterior border narrow. Hinge-line 

 arched and prolonged. Umbones thick, gibbose, incurved, not contiguous, some- 

 what elevated, placed in front of the middle line. No lunule or escutcheon. 

 Dorsal slope expanded and flattened. 



Interior. — Adductor muscle-scars large and rough. Casts show a deep groove 

 below the umbo for the peculiar hinge process. 



Exterior.— Surface almost smooth, but fine lines and stria? of growth are visible 

 with the microscope. 



Dimensions. — PL XXIV, fig. 3, a bivalved example, measures — 



Antero-posteriorly . . . .58 mm. 



Dorso-ventrally . . . .35 mm. 



From side to side (probably less as the valves are 



gaping) . . . . .32 mm. 



Locality. — From a bed of Calcareous shale at Burn Anne, Ayrshire. 



Observations. — E. acuta differs from all the other species of the genus in 

 possessing a very much narrowed posterior end. Casts show the peculiar shell- 

 process beneath the umbo, found in all species of the genus Edmondia. The species 

 is founded on three specimens in the collection of Mr. J. Smith, Kilwinning. 



Edmondia senilis, Phillips, sp., 1830. 



The type specimen, a right valve, is preserved in the University Museum, 

 Oxford. It appears to be a very large specimen of E. rudis, M'Coy, as I hinted, 

 p. 303, vol. i. The name E. rudis, M'Coy, therefore, is superseded by E. senilis 

 on the grounds of priority. 



