Paheozoic Bivalved Entomostraca. 185 



border straight and about two thirds of the valve-length ; 

 ventral border incurved and sloping downwards to maxi- 

 mum height, which is in the posterior third ; extremities 

 rounded, the posterior being the larger and more projecting. 

 The subcentral pit, which is transverse, is placed somewhat 

 nearest the dorsal and posterior portions of the valve. A 

 marginal rim bounds each valve, and is continued as a ridge 

 from the dorsal centre downwards, and concentrically with 

 the margins to or near the subcentral pit ; within the central 

 area thus formed is a longitudinal and somewhat sinuous 

 ridge, which is free at the ends. Edge view (fig. 11, b, 

 lateral contour) narrow, ovate, and rather constricted near the 

 centre. Surface smooth. Length ^V inch. 



This species does not vary among individuals much in 

 character, except perhaps a little in relative length. 



It appears to be confined to the lower portion of the Car- 

 boniferous series, where it is very abundant at some horizons, 

 as already noted (p. 176). 



K. spiralis has been described by one of us in the ' Proceed- 

 ings of the Berwickshire Naturalists' Club,' from somewhat 

 imperfect specimens collected by the late Mr. George Tate, of 

 Alnwick. 



Localities. — England. Lower Carboniferous: Tweedmouth, 

 Northumberland. Scar or Mountain Limestone : Meathop 

 (near Grange-over-Sands), Westmoreland; Calees, Cumber- 

 land. 



Scotland. Calciferous Sandstone : on the coast near the fol- 

 lowing places : — east of Pittenweem, Billow Ness, Kilminning, 

 Eanderstone, and Kingsbarns, in Fifeshire ; Oakbank Sand- 

 stone Quarry, Linlithgowshire. 



7. Kirkbya spinosa, Jones & Kirkby. (PI. III. figs. 

 12 a, b.) 



Kirkbya spinosa, J. & K., 1867, Trans. Geol. Soc. of Glasgow, vol. ii. 



p. 220 ; 1871, vol. iii. Suppl. p. 29. 

 Kirkbya spinosa, Armstrong and others, 1876, Catal. W.-Scot. Foss. 



p. 45. 



Ovate-oblong, oblique at the ends, swollen in front, rather 

 compressed behind, less than twice as high as long. Dorsal 

 border straight, and a fourth less than maximum length j 

 ventral border curved ; anterior extremity rounded and most 

 prominent above ; posterior extremity obliquely rounded and 

 most prominent below. The anterior portion of the valve is 

 much the thickest. The subcentral pit is sometimes longi- 

 tudinal, sometimes transverse and almost a sulcus, which is 

 occasionally divided by the upper ridge. Two, and even 



