36 CARBONIFEROUS LAMELLIBRANCTITATA. 



Limatulina scotica, sp. nov. Plate IX, figs. 1 — 5. 



Specific Characters. — Shell small, quadrately suborbicular, very inequivalve, sub- 

 auriculate. The right valve only slightly convex, the left triangularly gibbose and 

 compressed at the antero- and postero-snperior angles. The anterior and inferior 

 margins rounded, the posterior concavo-convex from above downwards. The hinge- 

 line straight, of medium length, forming well-marked angles at each extremity 

 with the anterior and posterior borders. The nmbones almost central, that of the 

 right valve small, not elevated, and inconspicuous, the left raised above the hinge- 

 line, gibbose and incurved. The anterior superior angle marked off in the 

 right valve, but a deep triangular slit reaching almost up to the umbo, for the 

 passage of the byssus, but marked off in the left valve by a more or less well- 

 defined groove. The posterior superior angle of both valves compressed and 

 subauriculate. 



Interior. — Below the umbo, in the left valve is a transverse groove which 

 received the cartilage ; that in the right valve is not so deep. 



Exterior. — The surface is ornamented with many simple fine radiating ribs and 

 sulci, whose regularity is at times interfered with by obscure lines of growth, 

 which are most marked towards the posterior superior angle. 



Dimensions. — PL IX, fig. 2, from Muirfoot Burn, New Cumnock, measures — 

 Antero-posteriorly . . . .21 mm. 



Dorso-ventrally . . . .20 mm. 



From side to side . . . .9 mm. 



Locality. — Upper Limestone series, Muirfoot Burn, New Cumnock, Ayrshire. 



Observations. — I have collected specimens of this species with Mr. J. Smith at 

 Muirfoot Burn, New Cumnock, where it is accompanied by Lingula mytiloides, 

 Nucula gibbosa, Nnculana laevistriata, N. attenuata, and Cardiomorpha limosa. None 

 of the specimens are quite perfect, but I have fortunately been able to obtain for 

 study and illustration bivalved examples, which show the characteristic features of 

 the genus. In these specimens the left valve very frequently has both ears 

 missing, and this imperfection gives quite a false idea of the antero-posterior 

 diameter of the valve at the hinge-line. The left umbo is very large, and quite 

 overlaps the diminutive one of the right valve. The hinge-line is elongate 

 and hollow, apparently not striated, and receives a cartilage which united the 

 valves. 



Singly, the valves might be mistaken for those small species of Aviculopecten 

 with fine radiating strias. 



