part 4] CAMBRIAN HORIZONS OF COMLEY. 341 



Lingulella Salter. 



LiNGULELLA VIRIDIS, Sp. 110V. (PI. XXII, figs. 10-12.) 



Type-specimen, a dorsal valve [97]. 



Diagnosis. — General form ovate, a little acuminate posteriorly ; 

 apical angle in the dorsal valve about 60°, in the ventral slightly 

 less ; the two valves are about equally convex ; area, in the dorsal 

 valve, apparently in the same plane as the margin of the valve, in 

 the ventral rising at a gentle angle. 



Exterior of both valves marked with from three to six principal 

 lines of growth, showing numerous, very fine, concentric stria? 

 between them, also many radiating strise only visible under a strong 

 magnifier. 



Interior of dorsal valve (only known from casts) with two 

 gently convex, curved ridges, extending over the middle third of 

 the length of the valve, convex towards the centre-line and 

 tapering to points anteriorly ; within these ridges and back to- 

 wards the apex the surface is roughened by minute projections, 

 outside them it is smooth and polished ; faint indications of linear 

 marks are sometimes visible in the roughened area, but no muscle- 

 scars have been detected. 



Area gently convex and, in the dorsal valve, separated by a very 

 narrow space from the umbonal portion of the shell ; marked by 

 three to six sinuous ridges that are strong as compared with the 

 concentric striae on the body of the shell. 



Dimensions. — The type-specimen has a length of 5 mm.; more 

 usually the shells are from 2 to 3 mm. in length. The convexity 

 is about - 2 of the length, and the width - 8 in dorsal valves and '7 in 

 ventral valves. 



Observations. — There is no good interior of the ventral valve. 

 Fig. 10 shows an internal cast from which the shell-substance has 

 been in part cleared away. 



In form and external characters the species seems near to 

 L. uathorsti Linnarsson ; but the internal marks of that species, so 

 far as known, and the details of the area of the dorsal valve are 

 very different. 



Locality and horizon. — Comkry, Lower Cambrian; from 

 the Strenuella Limestone, horizon Ac 4 , and sparingly from the 

 Protolenns Limestone, horizon Ac.. 



Lixgtjlella nicholsoni Callaway. 



Lingulella nicholsoni Callaway, 1874, Q.J.G.S. vol. xxx, p. 196. 



Lingulella nicholsoni Callaway, 1877, < J. J. G.S. vol. xxxiii, p. 668 & pi. xxiv r 



figs. 11, lla-llb. 

 Lingulella nicholsoni (Callaway), Wakott, 1912, U.S. Geol. Surv. Monogv. vol.li^ 



p. 522 & pi. xxx, figs 3, 3 a-3f. 



Dr. Callaway records 1 the discovery of this species, together 

 with ' the Shineton graptolites,' in shales east of Lawley Hill. 



1 1879, p. 759. 

 Q. J. G.S. No. 304. 2 b 



