NUCULA SCOTICA. 191 



A small specimen from the shales below the Millstone-grit, Todmorden, in the 

 Manchester Museum, Owens College, from the Gibson Collection, I think without 

 doubt belongs to Sowerby's species. 



Nocula Scotica, sp. nov., Hind. Plate XIV, figs. 37 — 39. 



Cf. Nucttla teivialis, JEichwald. Lethaea Rossica, pi. xxxviii, fig. 15. 



Specific Characters. — Shell small, gibbose, especially above, deltoid, oblique, 

 very inequilateral. The anterior end is short, swollen, and compressed from 

 before backwards, so that a cordiform anterior surface is apparent, bisected by 

 the lower elevation of the extreme edges of the valves. The anterior border 

 descends obliquely downwards and forwards, and is almost straight, joining the 

 inferior border at a marked obtusely rounded angle. The lower border is 

 regularly and almost semicircularly curved. The posterior border is oblique and 

 short, and the posterior-inferior angle is almost acute. 



The hinge-line is comparatively extensive, consisting of two parts, which meet 

 at an acute angle beneath the umbones. These are acute, incurved, and twisted 

 forwards, much elevated above the hinge-line, contiguous, and situated in the 

 anterior fourth of the shell. The valves are expanded laterally above, and the 

 dorsal slope is broad and very slightly hollowed. Elsewhere the contour of the 

 shell is regularly convex from above downwards and from before backwards. 



Interior. — The adductor scars have not yet been exposed. The hinge consists 

 of two sets of teeth, the posterior being the longer, placed at an acute angle to 

 each other, and separated below the umbo by a wide and deep cartilage-socket ; 

 the arrangement of the hinge-teeth themselves is normal. 



Exterior. — The surface is ornamented with close, regular, equidistant, concen- 

 tric, rounded lines and sulci, with here and there an occasional deeper concentric 

 groove. 



Dimensions. — PI. XIV, fig. 37, measures — 



Antero-posteriorly . . . .6 mm. 



Dorso-ventrally . . . .5 mm. 



From side to side . . . .4 mm. 



Localities. — Scotland : the Lower Limestone series of Craigenglen, Campsie ; 

 the horizon of the Hurlet Limestone, Wilkieston, Fifeshire. 



Observations. — This species does not appear to attain to any considerable size, 

 judging from a large number sent me for examination by Mr. Kirkby, of Leven, 

 which were obtained from "Wilkieston, Fife. 



The only British species which at all resembles N. Scotica is N. sequalis, 



