98 CARBONIFEROUS LAMELL1BRANCHIATA. 



Posidoniella minor, Brown, sp. 1841. Plate VI, figs. 15, 17, 18, 22, 23. 



Gervillia minor, Brown, 1841. Trans. Geol. Soc. Manchester, vol. i, p. 227, 



pi. vii, fig. 70. 

 — — — 1849. Illustr. Fossil Conckology, p. 165, pi. Ixi**, 



fig. 31. 

 Avicula sqtjamtjla, Brown, 1849. Ibid., p. 161, pi. lxviii, fig. 10. 

 Posidonia ? Gibsoni, Salter, 1862. Mem. Geol. Surv., Geol. country round 



Wigan, p. 35, fig. 1 a. 

 Geryillia minor, Bolton, 1895. Catal. Type Fossils Owens College, p. 12. 



Specific Characters. — Shell equivalve, compressed ; subquadrate, somewhat 

 oblique. The anterior end of the shell is obsolete, the shell being most tumid at 

 the extreme anterior edge, which is straight, and descends downwards, and only 

 to a very slight extent backwards, passing with a semicircular curve into the inferior 

 border, which is broad and convex downwards. The posterior border is obliquely 

 truncate, forming above an obtuse angle with the hinge-plate, and descending down- 

 wards and backward, at first straight, then becoming curved into the inferior border. 

 The hinge-line is straight, and a little shorter than the greatest transverse 

 diameter. The umbones are slightly swollen, pointed forwards, terminal, and 

 contiguous. The valves are equally and obliquely swollen from the umbones, the 

 swelling being more marked in the anterior part of the shell, and becoming more 

 expanded and less convex as it passes downwards. The valves appear to have 

 been much flattened at the inferior and posterior borders ; posterior to and above 

 the swelling the valves are compressed and expanded. 



Interior. — Unknown, 



Exterior. — The surface is covered by irregular concentric folds, crowded in 

 front, but becoming separated as they pass backwards. The periostracum is 

 wrinkled, and appears to extend beyond the margins of the shell. 



Dimensions. — Fig. 15, PI. YI, measures — 



Antero-posteriorly . . . .15 mm. 



Dorso-ventrally . . . .16 mm. 



Elevation of each valve . . .2 mm. 



Localities. — Lancashire : the Bullion Foot-mine, Lower Coal-measures, Trawden 

 Colne. Height's Hay, near Sharnyford ; near Rossendale, in shales below the 

 Old Lawrence or Tumbling Cob Rock, and about 100 feet above the Lower 

 Mountain-mine. Reap's Clough, Bacup, and at Green Clough, Portsmouth, in 

 shale over the Upper Foot-mine. Towers Clough, in a shale 18 inches above, 

 and thin coal which is immediately above the Upper Rough Rock. Yorkshire : 

 the Shales below the Millstone-grit of Marsden, Hebden Bridge, and Tod- 



