EDMONDIA LYELLII 301 



irregularly placed concentric ridges or depressions ; above these was a finely 

 punctate periostracum. Shell thick. 



Dimensions. — Fig. 4, PI. XXXI, a perfect right valve, measures — 



Antero-posteriorly . . . .65 mm. 



Dorso-ventrally . . . .58 mm. 



Elevation of valve . . . .18 mm. 



Localities. — England : Northumberland, the limestone of Lowick. The Middle 

 limestone, West Witton, "Wen sley dale ; the limestone of Poolvash, Isle of Man. 

 Scotland : Lower Limestone series of Newfield, High Blantyre ; of Craigenglen, 

 Campsie ; Swinlees ; Auchenskeith ; Dairy; Broadstone, Beith ; McDonald Lime- 

 stone series, Muirkirk; Craighall, Fife. Ireland: the Carboniferous Limestone 

 of Galway. 



Observations. — This species is founded on numerous very fine examples from 

 the localities named above, and has externally a strong resemblance to the genus 

 Cardiomorpha, but the possession of an ossicle attached to the hinge-plate and 

 the different position of the anterior adductor muscle-scars separate it from that 

 genus, the position of the anterior adductor muscle being lower down and more 

 remote from the margin than obtains in Cardiomorpha ; the shell is also thicker, 

 and the surface-markings stronger than in that genus. Fig. 5, PI. XXXI, 

 is a very fine example from Craighall, Fife, and is in the Museum of Science and 

 Art, Edinburgh, and I am indebted to Dr. Traquair for permission to figure the 

 specimen. Fig. 1, PI. XXXI, a specimen from the limestone of Beith, Ayrshire, 

 in the possession of Mr. R. Craig, shows that the species possessed a periostracum 

 with spotted markings, of which a view is given, PI. XXXI, fig. 1 a. At least one 

 other species of the genus, E. sulcata, has the same character ; but owing to the 

 fact that specimens of any of the species rarely occur which have the periostracum 

 preserved, indeed the majority are found in the condition of internal casts, this 

 character cannot be yet stated to be universal in the species of this genus. 



Fig. 3, PI. XXXI, a specimen from Beith, is in the cabinet of Dr. John 

 Young, of the Hunterian Museum, Glasgow, and shows the very thick and deep 

 groove for the ossicle, and the adductor muscle-scars and pallial line. 



Fortunately, I have been able to isolate the hinge in the specimen, fig. 2, PL 

 XXXI, belonging to the Geological Survey of Ireland; and fig. 4a, PI. XXXI, a 

 shell belonging to the Geological Society of Glasgow, also shows this portion of the 

 shell very well. Compared with other species of Edmondia, the shell of E. Li/rllii 

 was very thick, very much thicker than that of E. primaeva, a much larger shell. 



From E. oblonga, E. Lyellii is easily distinguished by its greater obliquity and 

 longer, narrower anterior end, and the orbicular shape of the shell. 



Dr. Traquair informs me that the specimen from Craighall, Fife, bears a label, 



in Fleming's handwriting, Venerupis Lyellii. I have, therefore, adopted this 



specific name. 



39 



