184 Messrs. Jones and Kirkby on the 



5. Kirlcbya plicata, Jones & Kirkby. 

 (PI. III. figs. 9 and 10, a, b.) 



Kirkbya ph'cata, J. & K., 1867, Trans. Geol. Soc. Glasgow, vol. ii. 



p. 221 ; 1871, vol. iii. Suppl. p. 28. 

 Kirkh/a plicata, Armstrong and others, 1876, Catal. W.-Scot. Foss. 



p. 45. 

 Kirkbya plicata, Kirkby, 1880, Q. J. G. S. vol. xxxvi. p. 588. 



Ovate to subovate, compressed, and considerably over half 

 as high as long. Dorsal border straight, and two thirds (or 

 more) of the maximum length ; ventral border boldly arched ; 

 anterior extremity rounded and decidedly the smaller, sloping 

 below ; posterior extremity boldly and obliquely rounded. 

 The subcentral pit is deep, transverse, and usually placed 

 rather posteriorly. A narrow but prominent rim bounds 

 the valves, and two sinuous ribs of equal size to the rim 

 cross the valve from their point of junction near the 

 antero-centre to near the hind margin or the postero-ventral 

 angle, where they again approach very nearly together. 

 These ribs divide the valve into dorsal, central, and ventral 

 areas. The edge-view (lateral contour) varies in different 

 specimens from flatly lenticular to subcuneiforin (tig. 10, b). 

 Surface smooth in most of our specimens, but in a few cases 

 finely reticulated. Length -jj inch. 



Some few examples of this species show a third rib not far 

 from the ventral border (fig. 9) . The subcentral pit varies 

 in size ; sometimes it is not seen at all, and occasionally it 

 takes more the form of a sulcus. 



K. plicata was discovered by the late Mr. Charles Moore, of 

 Bath, in the Carboniferous Limestone of Backwell, Somerset, 

 where it appears to be not at all rare. 



Localities. — England. Carboniferous Limestone : Back- 

 well, Charterhouse, Weston-super-Mare, in Somerset. 



Scotland. Calciferous Sandstone : Randerstone, Fife ; 

 Craiglockhart Quarry and Camps, in Edinburghshire ; Larris- 

 ton Quarry and Penton Bridge, in Roxburghshire. Carbon- 

 iferous-Limestone series : Campbelltown, Argyleshire ; White- 

 field New Quarry, Peeblesshire. 



6. Kirkbya spiralis, Jones & Kirkby. 

 (PL HI. figs. 11, a, b.) 



Kirkbya spiralis (J. & K. MS.), Kirkby, 1880, Quart. Journ. Geol. Soc. 



vol. xxxvi. pp. 564, 568, 573, 588. 

 Kirkbya sjnralis, Jones, 1884, Proc. Berwicksh. Nat. Club, vol. x. 



p 323, pi. ii. tigs. 12, 13. 



Carapace subovate or oblong, highest behind, compressed, 

 slightly lobate ; height half the length or more. Dorsal 



