190 CARBONIFEROUS LAMELLIBRANCHIATA. 



The anterior adductor scar is comparatively superficial, and is situated at the 

 upper and anterior angle of the shell, and is not marginal. The posterior adductor 

 scar is more conspicuous, deeper anteriorly than behind, and situated a little 

 distance within the posterior-superior angle. Above this scar, and somewhat 

 anterior to it, close to the edge of the valve, is a small punctate scar for one of 

 the pedal muscles, and in the umbonal cavity are two small, pits, evidently for the 

 insertion of muscle-bands. The pallial line is remote from the margin, and is 

 entire. 



The external surface is ornamented with fine concentric lines of growth. 

 Dimensions. — PI. XIV, fig. 34, a cast from Coalbrookdale, measures — 

 Antero-posteriorly . . . .8 mm. 



Dorso-ventrally .... 6*5 mm. 



From side to side .... 4*5 mm. 



Localities. — England: Pennystone Ironstone; Coal-measures, Coalbrookdale; 

 Congleton Edge, some 100 yards below the base of the Millstone-grit ; Todmorden, 

 shales below the base of the Millstone-grit. Scotland : Upper Limestone series, 

 Gare ; Robroyston ; Orchard. Lower Limestone series, Craigenglen : South Hill, 

 Campsie, Thornton, and Rae's Gill ; Carluke in shale above the Hosie Limestone. 

 Observations. — The fossils figured by Sowerby as N. sequalis (op. cit.) were in 

 the condition of casts, but a portion of the exterior is seen in an impression. 

 I have been fortunate enough to obtain one specimen from the original locality, and 

 this is figured, PI. XIV, fig. 35. 



I have referred to this species a number of little shells labelled N. lineata, 

 Phillips, in the collections of Mr. J. Neilson. Messrs. Young and Armstrong 

 reported several localities for N. lineata, and I suspect that they are the authority 

 for the determination used by Mr. Neilson, and consequently I have added the list 

 of localities quoted by them for N. sequalis. 



Phillips's work on ' The Palaeozoic Fossils of Cornwall and Devon ' was not 

 published until 1841 ; and consequently, if the species are identical, Sowerby's 

 name will have the precedence. The figures of N. lineata given by Phillips 

 ('Pal. Foss. Cornwall,' &c, p. 39, pi. xviii, fig. 64), and later by Whidborne 

 (' Devonian Fauna, South England,' vol. iii, pt. 1, 1896, p. 97, pi. x, figs. 13, 14), 

 differ very much from those of Sowerby, being evidently different in shape and 

 surface markings. Phillips's description is " deltoidal, convex, covered with striae 

 parallel to the margin, of which every third or fourth is much more prominent ; 

 margin plain within." 



Sowerby's description is " transversely elongated, convex, marked with 

 concentric ridges ; anterior side rounded ; posterior separated by a ridge and 

 truncated; beaks nearest the anterior side." 



I have not been able to ascertain the presence of the ridge mentioned above. 



