PSEUDAMUSIUM CONCENTRICO-LINEATUM. Ill 



the valve b y a wide, scimitar-shaped slit for the byssus ; the right posterior ear 

 almost obsolete. The left anterior ear ill-defined, rolled, and small; the posterior 

 ear still smaller. The umbones gibbose, subcentral, and pointed. 



In terior. — Unkn< iwn. 



Exterior. — The surface of both valves is ornamented with radiating hands of 

 colour, varying in width and number. The surface of the valves is almost smooth, 

 but the microscope shows fine concentric lines and striae. The anterior side of the 

 right valve shows close radiating ribs, which extend to the border, but become 

 gradually obsolete from before backwards. 



Dimensions. — PI. XVII, fig. lo, a left valve, measures— 



Antero-posteriorly . . . .25 mm. 



Dorso-ventrally . . . .21 mm. 



Convexity of valve . . . .5 mm. 



Localities.- — England : the Carboniferous Limestone of Park Hill and Castleton, 

 Derbyshire. Ireland : the Carboniferous Limestone of Little Island, co. Cork. 



Observations. — Mr. R. Etheridge, jun., re-described and figured Phillips's species. 

 He figured five specimens which are in the Museum of the Geological Survey, 

 Jermyn Street, and I am kindly permitted to figure four of them (PL XVII, 

 figs. 11 — 14). Unfortunately no single specimen is absolutely perfect, but at least 

 two are right valves. The posterior ears are almost obsolete, but the anterior 

 ears are well developed. 



The type of Avicula sublobata, Phillips, has unfortunately disappeared ; but, in 

 spite of the poor figure and meagre description, I think there is no doubt that 

 Mr. Etheridge, jun., was quite correct in referring his specimens to that species. 

 He discusses at length the peculiar size and number of the colour-bands as 

 indicated in the figures, and thinks that the shell shows some doubtful affinity to 

 Streblopteria, M'Coy ; but the absence of the large and expanded posterior ears at 

 once necessitates its removal from that genus. I therefore have placed it under 

 the arenus Pseudamusium. 



PSEUDAMUSIUM C0NCENTKJCO-LINEATUM, Sp. 110V. Plate XX, tigs. 7 — 10. 



Specific Characters. — Shell of medium size, equivalve, equilateral, almost 

 circular, moderately gibbose. The anterior, lower, and posterior margin formed 

 by a regular curve, almost circular in form. The hinge-line straight, of moderate 

 length. The umbones small, pointed, not raised, subcentral. The right anterior 

 ear well marked and separated from the valve by a deep byssal slit; that of the 

 left valve depressed, deep, and somewhat rolled. 'The posterior ears smaller than 



