APPENDIX. 177 



MoDiOLA Macadamii, Kinahan, 1878. Manual of the Greology of Ireland, pi. iii, 



fig. 4. 

 — STJBPAEALLELA, B. Etheridge, 1888. rossils British Palaeozoic, p. 285. 



Specific Characters. — Shell moderately convex, especially in front, transversely 

 oblong. Superior and inferior borders subparallel. The anterior end is short, 

 convexly swollen, and has an almost semicircular margin, passing gradually 

 below into the inferior border, which is straight, or with an almost obsolete 

 sinuation a little anterior to its centre. The posterior border is truncate, almost 

 straight above, rounded below. The hinge-line is straight and long. The 

 umbones are tumid, obtuse, elevated above the hinge-line, and continuous, slightly 

 excavated in front by a well-marked but small lunule ; and are situated very 

 anteriorly in the anterior one-sixth of the shell. The valves are convexly 

 swollen ; there is a shallow contraction which passes obliquely downward and 

 backward from the back to the lower margin, becoming wider as it uears the 

 lower edge of the valve, which indistinctly marks off the anterior from the 

 posterior part of the shell. Posterior to this sulcus the shell is diagonally swollen 

 from the umbo to the posterior inferior angle, the swelling becoming less marked as 

 it proceeds backwards. Above the swelling the valves are flattened and 

 compressed into the hinge-line and posterior border. 



Interior. — Casts show the usual arrangement of the adductor and accessory 

 muscle-scars. 



The hinge is edentulous, and consists of a thickened mass in front, strongly 

 connected with the shell, situated immediately below the umbo, which pro- 

 jects downwards, and is slightly bevelled at the expense of the upper portion, 

 and of a smooth elongated part posteriorly bevelled at the expense of the lower 

 margin. 



Exterior. — The surface is ornamented with many very fine, thread-like strige 

 and lines of growth parallel to the border of the valves. Shell thin. 



Dimensions. — The type-specimen, PI. XXI, fig. 2, measures — 



Antero-posteriorly .' . . . .25 mm. 



Dorso-ventrally .... 9'5 ,, 



Elevation of valve . , . . 4 ,, 



Distribution. — In Carboniferous shales at Ballynascreen, and Slieve Gullion, co. 

 Derry ; Clogher, co. Tyrone, and Ballycastle, co. Antrim. Lower Carboniferous 

 shales of co. Cork and co. Tipperary (Baily). 



Ohsemations. — This shell is very distinct from those named Modiola Macadamii 

 by Portlock, although he was not altogether of this opinion, for he says, " Though 

 this appears so very distinct a form from Modiola Macadamii, I am disposed to 

 think that they all merge one into the other." As a matter of fact two of the 

 varieties of M. Macadamii are very distinct indeed, and all are totally different 



